Revert "[C++11] Replace LLVM atomics with std::atomic."

Breaks the MSVC build.
DataStream.cpp(44): error C2552: 'llvm::Statistic::Value' : non-aggregates cannot be initialized with initializer list

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202731 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/ManagedStatic.cpp

@@ -13,6 +13,7 @@
 
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Config/config.h"
+#include "llvm/Support/Atomic.h"
 #include <cassert>
 using namespace llvm;
 
@@ -27,7 +28,7 @@ void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(),
       void* tmp = Creator ? Creator() : 0;
 
       TsanHappensBefore(this);
-      std::atomic_thread_fence(std::memory_order_seq_cst);
+      sys::MemoryFence();
 
       // This write is racy against the first read in the ManagedStatic
       // accessors. The race is benign because it does a second read after a

lib/Support/Statistic.cpp

@@ -76,7 +76,7 @@ void Statistic::RegisterStatistic() {
       StatInfo->addStatistic(this);
 
     TsanHappensBefore(this);
-    std::atomic_thread_fence(std::memory_order_seq_cst);
+    sys::MemoryFence();
     // Remember we have been registered.
     TsanIgnoreWritesBegin();
     Initialized = true;

lib/Support/Threading.cpp

@@ -13,8 +13,8 @@
 
 #include "llvm/Support/Threading.h"
 #include "llvm/Config/config.h"
+#include "llvm/Support/Atomic.h"
 #include "llvm/Support/Mutex.h"
-#include <atomic>
 #include <cassert>
 
 using namespace llvm;
@@ -31,7 +31,7 @@ bool llvm::llvm_start_multithreaded() {
 
   // We fence here to ensure that all initialization is complete BEFORE we
   // return from llvm_start_multithreaded().
-  std::atomic_thread_fence(std::memory_order_seq_cst);
+  sys::MemoryFence();
   return true;
 #else
   return false;
@@ -44,7 +44,7 @@ void llvm::llvm_stop_multithreaded() {
 
   // We fence here to insure that all threaded operations are complete BEFORE we
   // return from llvm_stop_multithreaded().
-  std::atomic_thread_fence(std::memory_order_seq_cst);
+  sys::MemoryFence();
 
   multithreaded_mode = false;
   delete global_lock;

lib/Support/Timer.cpp

@@ -81,14 +81,14 @@ raw_ostream *llvm::CreateInfoOutputFile() {
 static TimerGroup *DefaultTimerGroup = 0;
 static TimerGroup *getDefaultTimerGroup() {
   TimerGroup *tmp = DefaultTimerGroup;
-  std::atomic_thread_fence(std::memory_order_seq_cst);
+  sys::MemoryFence();
   if (tmp) return tmp;
   
   llvm_acquire_global_lock();
   tmp = DefaultTimerGroup;
   if (!tmp) {
     tmp = new TimerGroup("Miscellaneous Ungrouped Timers");
-    std::atomic_thread_fence(std::memory_order_seq_cst);
+    sys::MemoryFence();
     DefaultTimerGroup = tmp;
   }
   llvm_release_global_lock();