Fails to build with glibc 2.12.1 without this patch.

http://lists.gnu.org/archive/html/bug-m4/2010-05/msg00002.html

--- a/src/path.c
+++ b/src/path.c
@@ -22,6 +22,7 @@
 /* Handling of path search of included files via the builtins "include"
    and "sinclude".  */
 
 #include "m4.h"
+#include "sys/stat.h"
 
 struct includes
