[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/lib/Sema/SemaTemplateVariadic.cpp b/clang/lib/Sema/SemaTemplateVariadic.cpp
index d976265..f90bff6 100644
--- a/clang/lib/Sema/SemaTemplateVariadic.cpp
+++ b/clang/lib/Sema/SemaTemplateVariadic.cpp
@@ -937,7 +937,7 @@
   }
 
   std::unique_ptr<CorrectionCandidateCallback> clone() override {
-    return llvm::make_unique<ParameterPackValidatorCCC>(*this);
+    return std::make_unique<ParameterPackValidatorCCC>(*this);
   }
 };