AC_INCLUDES_DEFAULT isn't actually needed and it causes a QA warning.

https://bugs.gentoo.org/921033
--- a/configure.ac
+++ b/configure.ac
@@ -402,7 +402,6 @@ dnl Checks for typedefs, structures, and compiler characteristics.
 SILENT_BOX([Checking types])
 
 AC_HEADER_DIRENT
-AC_INCLUDES_DEFAULT
 AC_PROG_EGREP
 
 AC_CHECK_HEADERS_ONCE([sys/time.h])