Address some compile-time warnings in SDL 2.0

Also disable VERBOSE DEBUG output.

Note - Still a pair of nasty warnings about the following

 * ‘rsvg_handle_close’ is deprecated: Use
   'rsvg_handle_read_stream_sync' instead

 * passing argument 3 of ‘autoscale_copy_smear_free’ from incompatible
   pointer type (SDL_BlitSurface)

They should be addressed.

src/fonts.h

@@ -67,9 +67,13 @@
 #define SDL_mutex int
 #define SDL_CreateMutex() 0     // creates in released state
 #define SDL_DestroyMutex(lock)
+#ifndef SDL_mutexP
 #define SDL_mutexP(lock)        // take lock
+#endif
+#ifndef SDL_mutexV
 #define SDL_mutexV(lock)        // release lock
 #endif
+#endif
 
 #endif