Fixed Segmentation Fault in db_stress on OSX.

Summary:
This patch provides a simplier solution to the memory leak
issue identified in patch https://reviews.facebook.net/D43677,
where a static function local variable can be used instead of
using a global static unique_ptr.

Test Plan: run db_stress on mac

Reviewers: igor, sdong, anthony, IslamAbdelRahman, maykov

Reviewed By: maykov

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D43995

util/comparator.cc

@@ -85,23 +85,14 @@ class ReverseBytewiseComparatorImpl : public BytewiseComparatorImpl {
 
 }// namespace
 
-static port::OnceType once = LEVELDB_ONCE_INIT;
-static std::unique_ptr<const Comparator> bytewise;
-static std::unique_ptr<const Comparator> rbytewise;
-
-static void InitModule() {
-  bytewise.reset(new BytewiseComparatorImpl);
-  rbytewise.reset(new ReverseBytewiseComparatorImpl);
-}
-
 const Comparator* BytewiseComparator() {
-  port::InitOnce(&once, InitModule);
-  return bytewise.get();
+  static BytewiseComparatorImpl bytewise;
+  return &bytewise;
 }
 
 const Comparator* ReverseBytewiseComparator() {
-  port::InitOnce(&once, InitModule);
-  return rbytewise.get();
+  static ReverseBytewiseComparatorImpl rbytewise;
+  return &rbytewise;
 }
 
 }  // namespace rocksdb

util/thread_local.cc

@@ -149,14 +149,13 @@ ThreadLocalPtr::StaticMeta::StaticMeta() : next_instance_id_(0) {
   // of memory backing destructed statically-scoped objects. Perhaps
   // registering with atexit(3) would be more robust.
   //
-  // This is not required on Windows.
-#if !defined(OS_WIN)
+  // This is not required on Windows.  Also, it's not required on Mac
+  // as ThreadLocal is not supported in Mac.
+#if !defined(OS_MACOSX) && !defined(IOS_CROSS_COMPILE) && !defined(OS_WIN)
   static struct A {
     ~A() {
-#if defined(OS_MACOSX)
       ThreadData* tls_ =
         static_cast<ThreadData*>(pthread_getspecific(Instance()->pthread_key_));
-#endif
       if (tls_) {
         OnThreadExit(tls_);
       }