Make sure code is only compiled if the appropriate subsystem is enabled

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%401642

src/timer/mint/SDL_systimer.c

@@ -21,6 +21,8 @@
 */
 #include "SDL_config.h"
 
+#ifdef SDL_TIMER_MINT
+
 /*
  *	TOS/MiNT timer driver
  *	based on vbl vector
@@ -151,3 +153,5 @@ void SDL_SYS_StopTimer(void)
 {
 	return;
 }
+
+#endif /* SDL_TIMER_MINT */