Avoid an implicit declaration of mkdir in the fchownat probe.  Fixed
in gnulib upstream via:

commit 3c136a2cc38d71083f123231a8b9ad4b01930789
Author: Bruno Haible <bruno@clisp.org>
Date:   Thu Jan 24 23:51:11 2019 +0100

    fchownat: Fix compilation error on Android 4.3.
    
    * lib/unistd.in.h: Include <sys/stat.h> when module 'fchownat' is in
    use.
    * m4/fchownat.m4 (gl_FUNC_FCHOWNAT_DEREF_BUG,
    gl_FUNC_FCHOWNAT_EMPTY_FILENAME_BUG): Include also <sys/stat.h>.
    * doc/posix-functions/fchownat.texi: Mention the issue.

The patched filed is not included in the upstream Git repository for
patch, so presumably the next upstream release will sync the file from
gnulib and get the fix this way.

diff --git a/m4/fchownat.m4 b/m4/fchownat.m4
index 54c670c7037246a4..b1a1287f80c297a0 100644
--- a/m4/fchownat.m4
+++ b/m4/fchownat.m4
@@ -86,6 +86,7 @@ AC_DEFUN([gl_FUNC_FCHOWNAT_EMPTY_FILENAME_BUG],
        [AC_LANG_PROGRAM(
           [[#include <unistd.h>
             #include <fcntl.h>
+	    #include <sys/stat.h>
           ]],
           [[int fd;
             int ret;