Add more missing config.h #includes

Now that we use AC_SYS_LARGEFILE, we need to pull in config.h at least
whereever we use mmap().  Fixes at least the test-suite and simple-shm
on 32 bit systems.
diff --git a/src/xwayland/hash.c b/src/xwayland/hash.c
index d841883..54f3de9 100644
--- a/src/xwayland/hash.c
+++ b/src/xwayland/hash.c
@@ -32,6 +32,8 @@
  *    Keith Packard <keithp@keithp.com>
  */
 
+#include <config.h>
+
 #include <stdlib.h>
 #include <stdint.h>