openat: work around AIX 7.1 fstatat issue This should fix the problem that was not properly fixed in the previous change, dated 2011-08-30. * lib/fstatat.c: Include <sys/stat.h> twice, the first with __need_system_stat_h defined. (orig_fstatat) [HAVE_FSTATAT]: New function. (rpl_fstatat): Go back to the old way of doing things, except call orig_fstatat instead of fstatat. * m4/openat.m4 (gl_FUNC_FSTATAT): Remove unnecessary check for openat. Remove unnecessary check whether fstatat fills in st_size etc.