[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/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 2439232..03683ce 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -10472,7 +10472,7 @@
   if (!Parents)
     // We build the parent map for the traversal scope (usually whole TU), as
     // hasAncestor can escape any subtree.
-    Parents = llvm::make_unique<ParentMap>(*this);
+    Parents = std::make_unique<ParentMap>(*this);
   return Parents->getParents(Node);
 }