[tsan] Replace pthread_yield with sched_yield in lit tests

[kubamracek]

Summary

OS X doesn't have pthread_yield. Let's use sched_yield instead.

compiler-rt/trunk/test/tsan/atomic_free3.cc

 // RUN: %clangxx_tsan -O1 %s -o %t && %deflake %run %t | FileCheck %s
 #include "test.h"
 
 // Test for https://github.com/google/sanitizers/issues/602
 
 void *Thread(void *a) {
   __atomic_store_n((int*)a, 1, __ATOMIC_RELAXED);
   return 0;
 }
 
 int main() {
   int *a = new int(0);
   pthread_t t;
   pthread_create(&t, 0, Thread, a);
   while (__atomic_load_n(a, __ATOMIC_RELAXED) == 0)
-    pthread_yield();
+    sched_yield();
   delete a;
   pthread_join(t, 0);
 }
 
 // CHECK: WARNING: ThreadSanitizer: data race
 // CHECK:   Write
 // CHECK:     #0 operator delete
 // CHECK:     #1 main
 
 // CHECK:   Previous atomic write
 // CHECK:     #0 __tsan_atomic32_store
 // CHECK:     #1 Thread

compiler-rt/trunk/test/tsan/real_deadlock_detector_stress_test.cc

if (what < 4 && locked.size() < kMaxPerThread) {
         }
       }
       int id = (rand_r(&rnd) % (kMutexes - max_locked - 1)) + max_locked + 1;
       Mutex *m = &mtx[id];
       // init the mutex if necessary or acquire a reference
       for (;;) {
         int old = __atomic_load_n(&m->state, __ATOMIC_RELAXED);
         if (old == kStateLocked) {
-          pthread_yield();
+          sched_yield();
           continue;
         }
         int newv = old + 1;
         if (old == kStateNotInited)
           newv = kStateLocked;
         if (cas(&m->state, old, newv)) {
           if (old == kStateNotInited) {
             if ((err = pthread_rwlock_init(&m->m, 0))) {

compiler-rt/trunk/test/tsan/signal_errno.cc

 }
 
 static __attribute__((noinline)) void loop() {
   barrier_wait(&barrier);
   while (done == 0) {
     volatile char *p = (char*)malloc(1);
     p[0] = 0;
     free((void*)p);
-    pthread_yield();
+    sched_yield();
   }
 }
 
 int main() {
   barrier_init(&barrier, 2);
   mainth = pthread_self();
   struct sigaction act = {};
   act.sa_sigaction = &MyHandler;