New module 'fstatat', split off from module 'openat'.

New module 'fstatat', split off from module 'openat'.

* lib/openat.h (statat, lstatat): Enable only if GNULIB_FSTATAT is
defined.
* m4/fstatat.m4: New file. extracted from m4/openat.m4.
* m4/openat.m4 (gl_FUNC_OPENAT): Don't set GNULIB_FSTATAT. Don't invoke
gl_FUNC_FSTATAT.
(gl_FUNC_FSTATAT): Moved to m4/fstatat.m4.
* modules/fstatat: New file, extracted from modules/openat.
* modules/openat (Files): Remove lib/fstatat.c.
(Depends-on): Remove lstat.
(configure.ac): Remove AC_LIBOBJ of fstatat.
* modules/fstatat-tests: New file, extracted from modules/openat-tests.
* modules/openat-tests (Files): Remove tests/test-fstatat.c,
tests/test-lstat.h, tests/test-stat.h.
(Depends-on): Remove getcwd-lgpl.
(Makefile.am): Remove rules for test-fstatat.
* doc/posix-functions/fstatat.texi: Mention module 'fstatat' instead
of module 'openat'.
* NEWS: Mention the change.
* modules/getcwd (Depends-on): Add fstatat.
* modules/linkat (Depends-on): Likewise.
* modules/mkfifoat-tests (Depends-on): Likewise.
* modules/utimensat (Depends-on): Add fstatat. Remove openat.