Legacy: Ensure stddef.h is present for size_t

Many compilers won't need this, but better to
have it so it's correct.

include/icsneo/icsneolegacy.h

@@ -5,6 +5,7 @@
 #include "icsneo/platform/tchar.h"
 
 #include <stdint.h>
+#include <stddef.h>
 typedef uint8_t byte; // Typedef helper for the following include
 #include "icsneo/icsnVC40.h" // Definitions for structs
 
@@ -166,4 +167,4 @@ extern int LegacyDLLExport icsneoDisableBitSmash(void* hObject, unsigned int res
 } // extern "C"
 #endif
 
-#endif
+#endif