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

diff --git a/objects/dib.c b/objects/dib.c
index 5c4e8a3..29f8090 100644
--- a/objects/dib.c
+++ b/objects/dib.c
@@ -6,6 +6,7 @@
  */
 
 #include <stdlib.h>
+#include <string.h>
 
 #include "winbase.h"
 #include "bitmap.h"