Fix compilation on Debian kFreeBSD.

The configure script correctly detects that utimensat() and futimens()
are missing but the headers define stub versions of the functions.
Including sys/stat.h pulls in the system definitions  so we can override
them safely.  Bug #1021.

include/sudo_compat.h

@@ -25,6 +25,7 @@
 #define SUDO_COMPAT_H
 
 #include <sys/types.h>	/* for gid_t, mode_t, size_t, ssize_t, time_t, uid_t */
+#include <sys/stat.h>	/* to avoid problems with mismatched headers and libc */
 #include <unistd.h>	/* to avoid problems with mismatched headers and libc */
 #include <stdio.h>
 #if !defined(HAVE_VSNPRINTF) || !defined(HAVE_VASPRINTF) || \