As promised in the --enable-host-pie patch, this patch adds another
configure option, --enable-host-bind-now, which adds -z now when linking
the compiler executables in order to extend hardening.  BIND_NOW with RELRO
allows the GOT to be marked RO; this prevents GOT modification attacks.

This option does not affect linking of target libraries; you can use
LDFLAGS_FOR_TARGET=-Wl,-z,relro,-z,now to enable RELRO/BIND_NOW.

With this patch:
$ readelf -Wd cc1{,plus,obj,gm2} f951 lto1 cpp  rust1 gnat1 | grep FLAGS
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE

c++tools/ChangeLog:

	* configure.ac (--enable-host-bind-now): New check.
	* configure: Regenerate.

gcc/ChangeLog:

	* configure.ac (--enable-host-bind-now): New check.  Add
	-Wl,-z,now to LD_PICFLAG if --enable-host-bind-now.
	* configure: Regenerate.
	* doc/install.texi: Document --enable-host-bind-now.

lto-plugin/ChangeLog:

	* configure.ac (--enable-host-bind-now): New check.  Link with
	-z,now.
	* configure: Regenerate.

[ This is my third attempt to add this configure option.  The first
version was approved but it came too late in the development cycle.
The second version was also approved, but I had to revert it:
<https://gcc.gnu.org/pipermail/gcc-patches/2022-November/607082.html>.
I've fixed the problem (by moving $(PICFLAG) from INTERNAL_CFLAGS to
ALL_COMPILERFLAGS).  Another change is that since r13-4536 I no longer
need to touch Makefile.def, so this patch is simplified. ]

This patch implements the --enable-host-pie configure option which
makes the compiler executables PIE.  This can be used to enhance
protection against ROP attacks, and can be viewed as part of a wider
trend to harden binaries.

It is similar to the option --enable-host-shared, except that --e-h-s
won't add -shared to the linker flags whereas --e-h-p will add -pie.
It is different from --enable-default-pie because that option just
adds an implicit -fPIE/-pie when the compiler is invoked, but the
compiler itself isn't PIE.

Since r12-5768-gfe7c3ecf, PCH works well with PIE, so there are no PCH
regressions.

When building the compiler, the build process may use various in-tree
libraries; these need to be built with -fPIE so that it's possible to
use them when building a PIE.  For instance, when --with-included-gettext
is in effect, intl object files must be compiled with -fPIE.  Similarly,
when building in-tree gmp, isl, mpfr and mpc, they must be compiled with
-fPIE.

With this patch and --enable-host-pie used to configure gcc:

$ file gcc/cc1{,plus,obj,gm2} gcc/f951 gcc/lto1 gcc/cpp gcc/go1 gcc/rust1 gcc/gnat1
gcc/cc1:     ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=98e22cde129d304aa6f33e61b1c39e144aeb135e, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/cc1plus: ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=859d1ea37e43dfe50c18fd4e3dd9a34bb1db8f77, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/cc1obj:  ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=1964f8ecee6163182bc26134e2ac1f324816e434, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/cc1gm2:  ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=a396672c7ff913d21855829202e7b02ecf42ff4c, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/f951:    ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=59c523db893186547ac75c7a71f48be0a461c06b, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/lto1:    ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=084a7b77df7be2d63c2d4c655b5bbc3fcdb6038d, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/cpp:     ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=3503bf8390d219a10d6653b8560aa21158132168, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/go1:     ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=988cc673af4fba5dcb482f4b34957b99050a68c5, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/rust1:   ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=b6a5d3d514446c4dcdee0707f086ab9b274a8a3c, for GNU/Linux 3.2.0, with debug_info, not stripped
gcc/gnat1:   ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=bb11ccdc2c366fe3fe0980476bcd8ca19b67f9dc, for GNU/Linux 3.2.0, with debug_info, not stripped

I plan to add an option to link with -Wl,-z,now.

Bootstrapped on x86_64-pc-linux-gnu with --with-included-gettext
--enable-host-pie as well as without --enable-host-pie.  Also tested
on a Debian system where the system gcc was configured with
--enable-default-pie.

Co-Authored by: Iain Sandoe  <iain@sandoe.co.uk>

ChangeLog:

	* configure.ac (--enable-host-pie): New check.  Set PICFLAG after this
	check.
	* configure: Regenerate.

c++tools/ChangeLog:

	* Makefile.in: Rename PIEFLAG to PICFLAG.  Set LD_PICFLAG.  Use it.
	Use pic/libiberty.a if PICFLAG is set.
	* configure.ac (--enable-default-pie): Set PICFLAG instead of PIEFLAG.
	(--enable-host-pie): New check.
	* configure: Regenerate.

fixincludes/ChangeLog:

	* Makefile.in: Set and use PICFLAG and LD_PICFLAG.  Use the "pic"
	build of libiberty if PICFLAG is set.
	* configure.ac:
	* configure: Regenerate.

gcc/ChangeLog:

	* Makefile.in: Set LD_PICFLAG.  Use it.  Set enable_host_pie.
	Remove NO_PIE_CFLAGS and NO_PIE_FLAG.  Pass LD_PICFLAG to
	ALL_LINKERFLAGS.  Use the "pic" build of libiberty if --enable-host-pie.
	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG and LD_PICFLAG after this
	check.
	* configure: Regenerate.
	* doc/install.texi: Document --enable-host-pie.

gcc/ada/ChangeLog:

	* gcc-interface/Make-lang.in (ALL_ADAFLAGS): Remove NO_PIE_CFLAGS.  Add
	PICFLAG.  Use PICFLAG when building ada/b_gnat1.o and ada/b_gnatb.o.
	* gcc-interface/Makefile.in: Use pic/libiberty.a if PICFLAG is set.
	Remove NO_PIE_FLAG.

gcc/m2/ChangeLog:

	* Make-lang.in: New var, GM2_PICFLAGS.  Use it.

gcc/d/ChangeLog:

	* Make-lang.in: Remove NO_PIE_CFLAGS.

intl/ChangeLog:

	* Makefile.in: Use @PICFLAG@ in COMPILE as well.
	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG after this check.
	* configure: Regenerate.

libcody/ChangeLog:

	* Makefile.in: Pass LD_PICFLAG to LDFLAGS.
	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG and LD_PICFLAG after this
	check.
	* configure: Regenerate.

libcpp/ChangeLog:

	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG after this check.
	* configure: Regenerate.

libdecnumber/ChangeLog:

	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG after this check.
	* configure: Regenerate.

libiberty/ChangeLog:

	* configure.ac: Also set shared when enable_host_pie.
	* configure: Regenerate.

zlib/ChangeLog:

	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG after this check.
	* configure: Regenerate.

The c++tools makefile doesn't remove progressively more files in each of
mostlyclean, clean, and distclean. Instead, each removes a different set
of files (and some files are not removed by any target). Use
prerequisites so that everything is removed.

Also, building in the $objdir/c++tools directory doesn't work, because
the INSTALL variable is never set. It works when building from the
top-level because INSTALL is set in the environment when recursively
invoking make for sub-directories.

c++tools/ChangeLog:

	PR bootstrap/101834
	* Makefile.in (INSTALL): Set variable.
	(mostlyclean): Mark as a phony target.
	(clean): Add mostlyclean as a prerequisite.
	(distclean): Add clean as a prerequisite and remove more files.
	(maintainer-clean): Add distclean as a prerequisite.

Select and FD_ISSET are declared in sys/time.h on most versions
of hpux.  As a result, HAVE_PSELECT and HAVE_SELECT can be 0.

2023-01-08  John David Anglin  <danglin@gcc.gnu.org>

c++tools/ChangeLog:

	PR other/107616
	* server.cc (server): Don't call FD_ISSET when HAVE_PSELECT
	and HAVE_SELECT are zero.

2022 -> 2023

This reverts commit 251c72a6.

This reverts commit 258d7149.

As promised in the --enable-host-pie patch, this patch adds another
configure option, --enable-host-bind-now, which adds -z now when linking
the compiler executables in order to extend hardening.  BIND_NOW with RELRO
allows the GOT to be marked RO; this prevents GOT modification attacks.

This option does not affect linking of target libraries; you can use
LDFLAGS_FOR_TARGET=-Wl,-z,relro,-z,now to enable RELRO/BIND_NOW.

c++tools/ChangeLog:

	* configure.ac (--enable-host-bind-now): New check.
	* configure: Regenerate.

gcc/ChangeLog:

	* configure.ac (--enable-host-bind-now): New check.  Add
	-Wl,-z,now to LD_PICFLAG if --enable-host-bind-now.
	* configure: Regenerate.
	* doc/install.texi: Document --enable-host-bind-now.

lto-plugin/ChangeLog:

	* configure.ac (--enable-host-bind-now): New check.  Link with
	-z,now.
	* configure: Regenerate.

This patch implements the --enable-host-pie configure option which
makes the compiler executables PIE.  This can be used to enhance
protection against ROP attacks, and can be viewed as part of a wider
trend to harden binaries.

It is similar to the option --enable-host-shared, except that --e-h-s
won't add -shared to the linker flags whereas --e-h-p will add -pie.
It is different from --enable-default-pie because that option just
adds an implicit -fPIE/-pie when the compiler is invoked, but the
compiler itself isn't PIE.

Since r12-5768-gfe7c3ecf, PCH works well with PIE, so there are no PCH
regressions.

When building the compiler, the build process may use various in-tree
libraries; these need to be built with -fPIE so that it's possible to
use them when building a PIE.  For instance, when --with-included-gettext
is in effect, intl object files must be compiled with -fPIE.  Similarly,
when building in-tree gmp, isl, mpfr and mpc, they must be compiled with
-fPIE.

I plan to add an option to link with -Wl,-z,now.

ChangeLog:

	* Makefile.def: Pass $(PICFLAG) to AM_CFLAGS for gmp, mpfr, mpc, and
	isl.
	* Makefile.in: Regenerate.
	* Makefile.tpl: Set PICFLAG.
	* configure.ac (--enable-host-pie): New check.  Set PICFLAG after this
	check.
	* configure: Regenerate.

c++tools/ChangeLog:

	* Makefile.in: Rename PIEFLAG to PICFLAG.  Set LD_PICFLAG.  Use it.
	Use pic/libiberty.a if PICFLAG is set.
	* configure.ac (--enable-default-pie): Set PICFLAG instead of PIEFLAG.
	(--enable-host-pie): New check.
	* configure: Regenerate.

fixincludes/ChangeLog:

	* Makefile.in: Set and use PICFLAG and LD_PICFLAG.  Use the "pic"
	build of libiberty if PICFLAG is set.
	* configure.ac:
	* configure: Regenerate.

gcc/ChangeLog:

	* Makefile.in: Set LD_PICFLAG.  Use it.  Set enable_host_pie.
	Remove NO_PIE_CFLAGS and NO_PIE_FLAG.  Pass LD_PICFLAG to
	ALL_LINKERFLAGS.  Use the "pic" build of libiberty if --enable-host-pie.
	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG and LD_PICFLAG after this
	check.
	* configure: Regenerate.
	* doc/install.texi: Document --enable-host-pie.

gcc/d/ChangeLog:

	* Make-lang.in: Remove NO_PIE_CFLAGS.

intl/ChangeLog:

	* Makefile.in: Use @PICFLAG@ in COMPILE as well.
	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG after this check.
	* configure: Regenerate.

libcody/ChangeLog:

	* Makefile.in: Pass LD_PICFLAG to LDFLAGS.
	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG and LD_PICFLAG after this
	check.
	* configure: Regenerate.

libcpp/ChangeLog:

	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG after this check.
	* configure: Regenerate.

libdecnumber/ChangeLog:

	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG after this check.
	* configure: Regenerate.

libiberty/ChangeLog:

	* configure.ac: Also set shared when enable_host_pie.
	* configure: Regenerate.

zlib/ChangeLog:

	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG after this check.
	* configure: Regenerate.

Some versions of the BSD getaddrinfo() call do not work with the specific
input of "0" for the servname entry (a segv results).  Since we are making
the call with a dummy port number, the value is actually no important, other
than it should be in range.  Work around the BSD bug by using "1" instead.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>

c++tools/ChangeLog:

	* server.cc (accept_from): Use "1" as the dummy port number.

Do this separately from all other Copyright updates, as ChangeLog files
can be modified only separately.

The allocated memory is not freed when returning early due to an error.

c++tools/ChangeLog:

	* resolver.cc (module_resolver::read_tuple_file): Use unique_ptr
	to ensure memory is freed before returning.

Closes #102663

ChangeLog:

	PR other/102663
	* Makefile.def: Handle install-dvi target.
	* Makefile.tpl: Likewise.
	* Makefile.in: Regenerate.

c++tools/ChangeLog:

	PR other/102663
	* Makefile.in: Add dummy install-dvi target.

gcc/ChangeLog:

	PR other/102663
	* Makefile.in: Handle dvidir and install-dvi target.
	* configure: Regenerate.
	* configure.ac: Add install-dvi to target_list.

gcc/ada/ChangeLog:

	PR other/102663
	* gcc-interface/Make-lang.in: Allow dvi-formatted
	documentation to be installed.

gcc/c/ChangeLog:

	PR other/102663
	* Make-lang.in: Add dummy c.install-dvi target.

gcc/cp/ChangeLog:

	PR other/102663
	* Make-lang.in: Add dummy c++.install-dvi target.

gcc/d/ChangeLog:

	PR other/102663
	* Make-lang.in: Allow dvi-formatted documentation
	to be installed.

gcc/fortran/ChangeLog:

	PR other/102663
	* Make-lang.in: Allow dvi-formatted documentation
	to be installed.

gcc/lto/ChangeLog:

	PR other/102663
	* Make-lang.in: Add dummy lto.install-dvi target.

gcc/objc/ChangeLog:

	PR other/102663
	* Make-lang.in: Add dummy objc.install-dvi target.

gcc/objcp/ChangeLog:

	PR other/102663
	* Make-lang.in: Add dummy objc++.install-dvi target.

gnattools/ChangeLog:

	PR other/102663
	* Makefile.in: Add dummy install-dvi target.

libada/ChangeLog:

	PR other/102663
	* Makefile.in: Add dummy install-dvi target.

libcpp/ChangeLog:

	PR other/102663
	* Makefile.in: Add dummy install-dvi target.

libdecnumber/ChangeLog:

	PR other/102663
	* Makefile.in: Add dummy install-dvi target.

libiberty/ChangeLog:

	PR other/102663
	* Makefile.in: Allow dvi-formatted documentation
	to be installed.

This just replies with "OK".

c++tools/ChangeLog:

	* resolver.cc (module_resolver::ModuleCompiledRequest):
	Add a simple handler.
	* resolver.h: Declare handler for ModuleCompiledRequest.

The c++tools configure fragments need to be built with a C++ compiler.

In addition, the stand-alone server uses diagnostic mechanisms in common
with GCC, but needs to define implementations for gcc_assert and
supporting output functions.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>

PR c++/98821 - modules : c++tools configures with CC but code fragments assume CXX.

	PR c++/98821

c++tools/ChangeLog:

	* config.h.in: Regenerate.
	* configure: Regenerate.
	* configure.ac: Configure using C++.  Pull logic to
	detect enabled checking modes; default to release
	checking.
	* server.cc (AI_NUMERICSERV): Define a fallback value.
	(gcc_assert): New.
	(gcc_unreachable): New.
	(fancy_abort): Only build when checking is enabled.

Co-authored-by: Jakub Jelinek <jakub@redhat.com>

This TU uses exit, but doesn't include <stdlib.h> or <cstdlib> and relies
on some other header to include it indirectly, which apparently doesn't
happen on reporter's host.

The other <c*> headers aren't guarded either and we rely on a compiler
capable of C++11, so maybe we can rely on <cstdlib> being around
unconditionally.

2021-05-25  Jakub Jelinek  <jakub@redhat.com>

	PR bootstrap/100731
	* server.cc: Include <cstdlib>.

c++tools/
	* configure.ac (--enable-maintainer-mode): Fix typo and weird syntax.
	* configure: Regenerate.

While looking at PR100731, I have noticed the copyright years are 2020-ish
only.  This patch adds it to update-copyright.py and updates those.

2021-05-25  Jakub Jelinek  <jakub@redhat.com>

contrib/
	* update-copyright.py: Add c++tools.
c++tools/
	* Makefile.in: Update copyright year.
	* configure.ac: Likewise.
	* resolver.cc: Likewise.
	* resolver.h: Likewise.
	* server.cc: Likewise.
	(print_version): Update copyright notice date.

c++tools/ChangeLog:

	* Makefile.in: Include also ../gcc folder.

gcc/ChangeLog:

	* Makefile.in: Rename gcov-iov to genversion and depend
	on version.h (instead of gcov-iov.h).
	* gcov-io.h: Include version.h instread of gcov-iov.h.
	* gengtype-state.c (read_state_version): Likewise.
	* gcov-iov.c: Moved to...
	* genversion.c: ...here.
	* lto-streamer.h (LTO_major_version): Define it with
	GCC_major_version.
	* version.c: Removed.
	* version.h: Removed.

libgcc/ChangeLog:

	* libgcov-driver.c (gcov_version): Use different name that does
	not clash with newly introduced macro.

It appears that many targets include the map header transitively in
other std headers included from system.h.  However there are some
editions of clang/libc++ in Xcode that do not, which results in a
bootstrap fail - since when resolver.h is included  there is then a
conflict in declaring abort().

The fix is to ensure that map is pulled in by system.h and before
resolver.h is included.  As a precautionary measure and to alert
anyone perhaps adding another header to resolver.h this patch also
gates the direct includes there on !IN_GCC.

c++tools/ChangeLog:

	* resolver.h: Do not include std headers directly when
	building in GCC.

gcc/cp/ChangeLog:

	* mapper-client.cc (INCLUDE_MAP): New; require map to be
	included from system.h.
	* mapper-resolver.cc (INCLUDE_MAP): Likewise.

PR98318 also pointed out that the NETWORKING #define was being checked
with both #if and #ifdef.  Let's consistently use one form.

	c++tools/
	* server.cc: Use #if NETWORKING not #ifdef, to be consistent
	with elsewhere.

With the introduction of C++20 modules and libcody, cc1plus and
cc1objplus gained a dependency on the socket functions.  Before those
were merged into libc in Solaris 11.4, one needed to link with -lsocket -lnsl
on Solaris, so that merge broke the Solaris 11.3 build.

While we already have 4 different checks for those libraries in the
tree, I decided to import autoconf-archive's AX_LIB_SOCKET_NSL macro
instead.  At the same time, the patch only links libcody and the
networking libs where needed (cc1plus, cc1objplus).

Bootstrapped without regressions on i386-pc-solaris2.11 (Solaris 11.3
and 11.4), sparc-sun-solaris2.11, and x86_64-pc-linux-gnu.

2020-12-16  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	c++tools:
	PR c++/98316
	* configure.ac: Include ../config/ax_lib_socket_nsl.m4.
	(NETLIBS): Determine using AX_LIB_SOCKET_NSL.
	* configure: Regenerate.
	* Makefile.in (NETLIBS): Define.
	(g++-mapper-server$(exeext)): Add $(NETLIBS).

	gcc/objcp:
	PR c++/98316
	* Make-lang.in (cc1objplus$(exeext)): Add $(CODYLIB), $(NETLIBS).

	gcc/cp:
	PR c++/98316
	* Make-lang.in (cc1plus$(exeext)): Add $(CODYLIB), $(NETLIBS).

	gcc:
	PR c++/98316
	* configure.ac (NETLIBS): Determine using AX_LIB_SOCKET_NSL.
	* aclocal.m4, configure: Regenerate.
	* Makefile.in (NETLIBS): Define.
	(BACKEND): Remove $(CODYLIB).

	config:
	PR c++/98316
	* ax_lib_socket_nsl.m4: Import from autoconf-archive.