SDL_malloc.c: workaround calling convention issues for real_xxx procs.

src/stdlib/SDL_malloc.c

@@ -5305,10 +5305,10 @@ History:
 #endif /* !HAVE_MALLOC */
 
 #ifdef HAVE_MALLOC
-#define real_malloc malloc
-#define real_calloc calloc
-#define real_realloc realloc
-#define real_free free
+static void* SDLCALL real_malloc(size_t s) { return malloc(s); }
+static void* SDLCALL real_calloc(size_t n, size_t s) { return calloc(n, s); }
+static void* SDLCALL real_realloc(void *p, size_t s) { return realloc(p,s); }
+static void  SDLCALL real_free(void *p) { free(p); }
 #else
 #define real_malloc dlmalloc
 #define real_calloc dlcalloc