Fixed warning when building on Windows

src/stdlib/SDL_stdlib.c

@@ -488,6 +488,9 @@ __declspec(selectany) int _fltused = 1;
 
 /* The optimizer on Visual Studio 2005 and later generates memcpy() and memset() calls */
 #if _MSC_VER >= 1400
+extern void *memcpy(void* dst, const void* src, size_t len);
+#pragma intrinsic(memcpy)
+
 #pragma function(memcpy)
 void *
 memcpy(void *dst, const void *src, size_t len)
@@ -495,13 +498,16 @@ memcpy(void *dst, const void *src, size_t len)
     return SDL_memcpy(dst, src, len);
 }
 
+extern void *memset(void* dst, int c, size_t len);
+#pragma intrinsic(memset)
+
 #pragma function(memset)
 void *
 memset(void *dst, int c, size_t len)
 {
     return SDL_memset(dst, c, len);
 }
-#endif
+#endif /* _MSC_VER >= 1400 */
 
 #ifdef _M_IX86