acconfig.h: Add _GLIBCXX_USE_C99_MATH.

	* acconfig.h: Add _GLIBCXX_USE_C99_MATH.
	* acinclude.m4 (GLIBCXX_ENABLE_C99): Define GLIBCXX_USE_C99_MATH.
	* configure.ac: Define HAVE_S_ISREG and HAVE_S_IFREG when
	targeting newlib.
	* aclocal.m4: Regenerated.
	* config.h.in: Likewise.
	* configure: Likewise.
	* Makefile.in: Likewise.
	* include/Makefile.in: Likewise.
	* libmath/Makefile.in: Likewise.
	* libsupc++/Makefile.in: Likewise.
	* testsuite/Makefile.in: Likewise.
	* src/Makefile.in: Likewise.
	* po/Makefile.in: Likewise.
	* include/c_std/std_cmath.h (_GLIBCXX_USE_C99): Replace with ...
	(_GLIBCXX_USE_C99_MATH): ... this.

	* testsuite/27_io/basic_filebuf/sgetn/char/1-in.cc: XFAIL for
	arm-none-elf.
	* testsuite/27_io/basic_filebuf/sgetn/char/1-io.cc: Likewise.
	* testsuite/27_io/basic_filebuf/sgetn/char/2-in.cc: Likewise.
	* testsuite/27_io/basic_filebuf/sgetn/char/2-io.cc: Likewise.
	* testsuite/27_io/basic_istream/readsome/char/6476-2.cc: Likewise.
	* testsuite/27_io/objects/char/9.cc: Likewise.
	* testsuite/ext/stdio_filebuf/char/10063-2.cc: Likewise.

From-SVN: r75209