Fixed a few broken includes.

diff --git a/win32/kernel32.c b/win32/kernel32.c
index 7f4b59a..3c44f39 100644
--- a/win32/kernel32.c
+++ b/win32/kernel32.c
@@ -8,6 +8,8 @@
  *      the function documentation for more details.
  */
 
+#include <string.h>
+
 #include "windef.h"
 #include "winbase.h"
 #include "wine/winbase16.h"