[llvm] 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.

llvm-svn: 369013
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
index fda19ee..3f5b5b8 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
@@ -263,5 +263,5 @@
 
 std::unique_ptr<MCObjectTargetWriter>
 llvm::createARMELFObjectWriter(uint8_t OSABI) {
-  return llvm::make_unique<ARMELFObjectWriter>(OSABI);
+  return std::make_unique<ARMELFObjectWriter>(OSABI);
 }