Windows: Just use WaitForSingleObjectEx() everywhere.

(It's supported on WinXP, no reason to have an #ifdef here...I think.)
diff --git a/src/thread/windows/SDL_systhread.c b/src/thread/windows/SDL_systhread.c
index 7f66cb3..2f22b89 100644
--- a/src/thread/windows/SDL_systhread.c
+++ b/src/thread/windows/SDL_systhread.c
@@ -199,11 +199,7 @@
 void
 SDL_SYS_WaitThread(SDL_Thread * thread)
 {
-#if __WINRT__
     WaitForSingleObjectEx(thread->handle, INFINITE, FALSE);
-#else
-    WaitForSingleObject(thread->handle, INFINITE);
-#endif
     CloseHandle(thread->handle);
 }