[C++11] Use std::atomic instead of LLVM's.

No intended functionality change.

llvm-svn: 202652

clang/lib/Basic/VirtualFileSystem.cpp

@@ -14,10 +14,10 @@
 #include "llvm/ADT/OwningPtr.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringExtras.h"
-#include "llvm/Support/Atomic.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/YAMLParser.h"
+#include <atomic>
 
 using namespace clang;
 using namespace clang::vfs;
@@ -828,8 +828,8 @@ vfs::getVFSFromYAML(MemoryBuffer *Buffer, SourceMgr::DiagHandlerTy DiagHandler,
 }
 
 UniqueID vfs::getNextVirtualUniqueID() {
-  static volatile sys::cas_flag UID = 0;
-  sys::cas_flag ID = llvm::sys::AtomicIncrement(&UID);
+  static std::atomic<unsigned> UID;
+  unsigned ID = ++UID;
   // The following assumes that uint64_t max will never collide with a real
   // dev_t value from the OS.
   return UniqueID(std::numeric_limits<uint64_t>::max(), ID);