Prefer new POSIX 200x interfaces over futimesat. * m4/utimens.m4 (gl_UTIMENS): Check for futimens, utimensat. * lib/utimens.c (gl_futimens): Use them for nanosecond resolution when available. [HAVE_BUGGY_NFS_TIME_STAMPS]: Allow C89 compilation. Signed-off-by: Eric Blake <ebb9@byu.net>