Replace llvm::MutexGuard/UniqueLock with their standard equivalents

All supported platforms have <mutex> now, so we don't need our own
copies any longer. No functionality change intended.

llvm-svn: 368149
diff --git a/clang/tools/libclang/Indexing.cpp b/clang/tools/libclang/Indexing.cpp
index bd511f1..36c0812 100644
--- a/clang/tools/libclang/Indexing.cpp
+++ b/clang/tools/libclang/Indexing.cpp
@@ -29,8 +29,8 @@
 #include "llvm/Support/CrashRecoveryContext.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Mutex.h"
-#include "llvm/Support/MutexGuard.h"
 #include <cstdio>
+#include <mutex>
 #include <utility>
 
 using namespace clang;
@@ -132,12 +132,12 @@
   }
 
   void copyTo(PPRegionSetTy &Set) {
-    llvm::MutexGuard MG(Mux);
+    std::lock_guard<llvm::sys::Mutex> MG(Mux);
     Set = ParsedRegions;
   }
 
   void update(ArrayRef<PPRegion> Regions) {
-    llvm::MutexGuard MG(Mux);
+    std::lock_guard<llvm::sys::Mutex> MG(Mux);
     ParsedRegions.insert(Regions.begin(), Regions.end());
   }
 };