tweak lstat.c to avoid mingw link failure

* gnulib/lib/lstat.c: Include <sys/stat.h> *before* the use of stat in
orig_stat.  Otherwise, on mingw (which lacks lstat), any program using
the lstat module would not get the redefinition-to-stat provided by
gnulib's sys/stat.h.  Reported by Daniel P. Berrange.

gnulib/lib/lstat.c

@@ -25,15 +25,15 @@
 #include <sys/stat.h>
 #undef __need_system_sys_stat_h
 
+/* Specification.  */
+#include <sys/stat.h>
+
 static inline int
 orig_lstat (const char *filename, struct stat *buf)
 {
   return lstat (filename, buf);
 }
 
-/* Specification.  */
-#include <sys/stat.h>
-
 #include <string.h>
 #include <errno.h>