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

diff --git a/msdos/dosaspi.c b/msdos/dosaspi.c
index dc457a9..29771cb 100644
--- a/msdos/dosaspi.c
+++ b/msdos/dosaspi.c
@@ -1,5 +1,6 @@
 #include "config.h"
 
+#include <string.h>
 #include "winbase.h"
 #include "wine/windef16.h"
 #include "wine/winaspi.h"