This patch updates GCC to use autoconf 2.69 and automake 1.15.1.
(That's not the latest automake version, but it's the one used by
binutils-gdb, with which consistency is desirable, and in any case
seems a useful incremental update that should make a future update to
1.16.1 easier.)

The changes are generally similar to the binutils-gdb ones, and are
copied from there where shared files and directories are involved
(there are some further changes to such shared directories, however,
which I'd expect to apply to binutils-gdb once this patch is in GCC).
Largely, obsolete AC_PREREQ calls are removed, while many
AC_LANG_SOURCE calls are added to avoid warnings from aclocal and
autoconf.  Multilib support is no longer included in core automake,
meaning that multilib.am needs copying from automake's contrib
directory into the GCC source tree.  Autoconf 2.69 has Go support, so
local copies of that support are removed.  I hope the D support will
s...