[Clang] Migrate llvm::make_unique to std::make_unique

Now that we've moved to C++14, we no longer need the llvm::make_unique
implementation from STLExtras.h. This patch is a mechanical replacement
of (hopefully) all the llvm::make_unique instances across the monorepo.

Differential revision: https://reviews.llvm.org/D66259

llvm-svn: 368942
diff --git a/clang/unittests/Sema/ExternalSemaSourceTest.cpp b/clang/unittests/Sema/ExternalSemaSourceTest.cpp
index c591ccb..edf91c9 100644
--- a/clang/unittests/Sema/ExternalSemaSourceTest.cpp
+++ b/clang/unittests/Sema/ExternalSemaSourceTest.cpp
@@ -187,7 +187,7 @@
   std::unique_ptr<clang::ASTConsumer>
   CreateASTConsumer(clang::CompilerInstance &Compiler,
                     llvm::StringRef /* dummy */) override {
-    return llvm::make_unique<clang::ASTConsumer>();
+    return std::make_unique<clang::ASTConsumer>();
   }
 
   void ExecuteAction() override {