threads.c: re-enable code to set the stack size on posix. Default stack size on OS X 10.10 isn't large enough

common/threads.c

@@ -233,11 +233,9 @@ RunThreadsOn(int start, int workcnt, void *(func)(void *), void *arg)
     status = pthread_attr_init(&attrib);
     if (status)
 	Error("pthread_attr_init failed");
-#if 0
     status = pthread_attr_setstacksize(&attrib, 0x100000);
     if (status)
 	Error("pthread_attr_setstacksize failed");
-#endif
 
     threads = malloc(sizeof(*threads) * numthreads);
     if (!threads)