[tsan] Change mutexset6.cc to use a mutex instead of spinlock

[kubamracek]

Summary

Pthread spinlocks are not available on OS X.

test/tsan/mutexset6.cc

 // RUN: %clangxx_tsan -O1 %s -o %t && %deflake %run %t | FileCheck %s
 #include "test.h"
 
 int Global;
 pthread_mutex_t mtx1;
-pthread_spinlock_t mtx2;
+pthread_mutex_t mtx2;
 pthread_rwlock_t mtx3;
 
 void *Thread1(void *x) {
   barrier_wait(&barrier);
   pthread_mutex_lock(&mtx1);
   Global++;
   pthread_mutex_unlock(&mtx1);
   return NULL;
 }
 
 void *Thread2(void *x) {
   pthread_mutex_lock(&mtx1);
   pthread_mutex_unlock(&mtx1);
-  pthread_spin_lock(&mtx2);
+  pthread_mutex_lock(&mtx2);
   pthread_rwlock_rdlock(&mtx3);
   Global--;
-  pthread_spin_unlock(&mtx2);
+  pthread_mutex_unlock(&mtx2);
   pthread_rwlock_unlock(&mtx3);
   barrier_wait(&barrier);
   return NULL;
 }
 
 int main() {
   barrier_init(&barrier, 2);
   // CHECK: WARNING: ThreadSanitizer: data race
   // CHECK:   Write of size 4 at {{.*}} by thread T1
   // CHECK:                          (mutexes: write [[M1:M[0-9]+]]):
   // CHECK:   Previous write of size 4 at {{.*}} by thread T2
   // CHECK:               (mutexes: write [[M2:M[0-9]+]], read [[M3:M[0-9]+]]):
   // CHECK:   Mutex [[M1]] (0x{{.*}}) created at:
   // CHECK:     #1 main {{.*}}mutexset6.cc:[[@LINE+5]]
   // CHECK:   Mutex [[M2]] (0x{{.*}}) created at:
   // CHECK:     #1 main {{.*}}mutexset6.cc:[[@LINE+4]]
   // CHECK:   Mutex [[M3]] (0x{{.*}}) created at:
   // CHECK:     #1 main {{.*}}mutexset6.cc:[[@LINE+3]]
   pthread_mutex_init(&mtx1, 0);
-  pthread_spin_init(&mtx2, 0);
+  pthread_mutex_init(&mtx2, 0);
   pthread_rwlock_init(&mtx3, 0);
   pthread_t t[2];
   pthread_create(&t[0], NULL, Thread1, NULL);
   pthread_create(&t[1], NULL, Thread2, NULL);
   pthread_join(t[0], NULL);
   pthread_join(t[1], NULL);
   pthread_mutex_destroy(&mtx1);
-  pthread_spin_destroy(&mtx2);
+  pthread_mutex_destroy(&mtx2);
   pthread_rwlock_destroy(&mtx3);
 }