N3DS: Semaphore fixes. (#6776)

* N3DS: Make Sem waits cooperative friendly.

The 3DS has a cooperative threading model. Sleeping after TryWait and
WaitTimeout avoid starving other threads. It inccurs a runtime penalty,
but it's better than having to hard reset your console to recover from
a deadlock.

test/testsem.c

@@ -208,6 +208,8 @@ TestOverheadContended(SDL_bool try_wait)
         }
         /* Make sure threads consumed everything */
         while (SDL_SemValue(sem)) {
+            /* Friendlier with cooperative threading models */
+            SDL_DelayNS(1);
         }
     }
     end_ticks = SDL_GetTicks();