* m4/jm-macros.m4 (gl_MACROS): Call cu_PREREQ_STAT_PROG rather

* m4/jm-macros.m4 (gl_MACROS): Call cu_PREREQ_STAT_PROG rather
than AC_REQUIREing, so that sys/mount.h isn't tested for after
the test result.  I'm not sure why this fix is needed, but it
works.
* m4/stat-prog.m4 (cu_PREREQ_STAT_PROG): Revamp to reflect better
what stat.c actually needs.
* src/stat.c: Include <stddef.h>
(alignof): New macro.
(HAVE_STRUCT_STATXFS_F_FSID___VAL, HAVE_STRUCT_STATXFS_F_FSID_VAL):
Remove.
(STRUCT_STATXFS_F_FSID_IS_INTEGER): New macro.
(FSID_VAL): Remove.
(print_statfs): If f_fsid isn't an integer, grab its words one
at a time in little-endian order.  This is a bit easier to configure
and should avoid a compilation failure on MacOS reported by Bruno
Haible.