Fixed compile error using Borland C++

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%404465

src/thread/win32/SDL_systhread.c

@@ -80,7 +80,7 @@ typedef struct ThreadStartParms
     pfnSDL_CurrentEndThread pfnCurrentEndThread;
 } tThreadStartParms, *pThreadStartParms;
 
-static unsigned __stdcall
+static DWORD __stdcall
 RunThread(void *data)
 {
     pThreadStartParms pThreadParms = (pThreadStartParms) data;