Removed SDL_bool in favor of plain bool

We require stdbool.h in the build environment, so we might as well use the plain bool type.

If your environment doesn't have stdbool.h, this simple replacement will suffice:
typedef signed char bool;

src/SDL_log.c

@@ -446,7 +446,7 @@ static const char *GetLogPriorityPrefix(SDL_LogPriority priority)
     }
 }
 
-SDL_bool SDL_SetLogPriorityPrefix(SDL_LogPriority priority, const char *prefix)
+bool SDL_SetLogPriorityPrefix(SDL_LogPriority priority, const char *prefix)
 {
     char *prefix_copy;