revert some more spin optimizations that turned out to be pessimizations

src/stdio/__lockfile.c

@@ -13,7 +13,7 @@ void __lockfile(FILE *f)
 		f->lockcount++;
 		return;
 	}
-	while (f->lock || a_cas(&f->lock, 0, tid))
+	while (a_cas(&f->lock, 0, tid))
 		if (spins) spins--, a_spin();
 		else syscall(SYS_sched_yield);
 	f->lockcount = 1;

src/thread/pthread_spin_lock.c

@@ -2,6 +2,6 @@
 
 int pthread_spin_lock(pthread_spinlock_t *s)
 {
-	while (a_xchg(s, 1));
+	while (a_xchg(s, 1)) a_spin();
 	return 0;
 }

src/thread/pthread_spin_trylock.c

@@ -2,6 +2,5 @@
 
 int pthread_spin_trylock(pthread_spinlock_t *s)
 {
-	if (*s || a_xchg(s, 1)) return EBUSY;
-	return 0;
+	return -a_xchg(s, 1) & EBUSY;
 }