The AC_CHECK_FUNCS tests cause the build to fail for bare metal cross
compilers, where link tests are not allowed. Replace them with
GCC_TRY_COMPILE_OR_LINK tests instead. Skip all the Filesystem
dependency checks if not building the filesystem library.

	* acinclude.m4 (GLIBCXX_CHECK_FILESYSTEM_DEPS): Only check when
	enable_libstdcxx_filesystem_ts = yes. Check for link, readlink and
	symlink.
	* config.h.in: Regenerate.
	* configure: Regenerate.
	* configure.ac: Remove AC_CHECK_FUNCS for link, readlink and symlink.

From-SVN: r261704