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/thread/windows/SDL_syssem.c

@@ -333,7 +333,7 @@ void SDL_DestroySemaphore(SDL_Semaphore *sem)
     SDL_sem_impl_active.Destroy(sem);
 }
 
-SDL_bool SDL_WaitSemaphoreTimeoutNS(SDL_Semaphore *sem, Sint64 timeoutNS)
+bool SDL_WaitSemaphoreTimeoutNS(SDL_Semaphore *sem, Sint64 timeoutNS)
 {
     return SDL_sem_impl_active.WaitTimeoutNS(sem, timeoutNS);
 }