Fixed bug 3745 - specify SDLCALL as the calling convention for API callbacks

Patches contributed by Ozkan Sezer

src/thread/SDL_thread.c

@@ -50,7 +50,7 @@ SDL_TLSGet(SDL_TLSID id)
 }
 
 int
-SDL_TLSSet(SDL_TLSID id, const void *value, void (*destructor)(void *))
+SDL_TLSSet(SDL_TLSID id, const void *value, void (SDLCALL *destructor)(void *))
 {
     SDL_TLSData *storage;
 

src/thread/SDL_thread_c.h

@@ -71,7 +71,7 @@ typedef struct {
     unsigned int limit;
     struct {
         void *data;
-        void (*destructor)(void*);
+        void (SDLCALL *destructor)(void*);
     } array[1];
 } SDL_TLSData;