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

diff --git a/dlls/comctl32/progress.c b/dlls/comctl32/progress.c
index 84915f8..0163694 100644
--- a/dlls/comctl32/progress.c
+++ b/dlls/comctl32/progress.c
@@ -6,6 +6,7 @@
  *
  */
 
+#include <string.h>
 #include "winbase.h"
 #include "commctrl.h"
 #include "debugtools.h"