Added a hint to specify new thread stack size (thanks, Gabriel!).

Fixes Bugzilla #2019.

(we'll do a better fix when we break the API in SDL 2.1.)

test/torturethread.c

@@ -87,6 +87,8 @@ main(int argc, char *argv[])
         SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't initialize SDL: %s\n", SDL_GetError());
         return (1);
     }
+    
+    SDL_SetHintWithPriority(SDL_HINT_THREAD_STACK_SIZE, SDL_getenv(SDL_HINT_THREAD_STACK_SIZE), SDL_HINT_OVERRIDE);
 
     signal(SIGSEGV, SIG_DFL);
     for (i = 0; i < NUMTHREADS; i++) {