Add <string.h> to files that needed it.

diff --git a/memory/codepage.c b/memory/codepage.c
index 142d693..9c6d54d 100644
--- a/memory/codepage.c
+++ b/memory/codepage.c
@@ -7,6 +7,7 @@
 #include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 
 #include "winbase.h"
 #include "winerror.h"