[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/AMDGPU/GCNIterativeScheduler.cpp b/llvm/lib/Target/AMDGPU/GCNIterativeScheduler.cpp
index 3525174..90ab6a1 100644
--- a/llvm/lib/Target/AMDGPU/GCNIterativeScheduler.cpp
+++ b/llvm/lib/Target/AMDGPU/GCNIterativeScheduler.cpp
@@ -237,7 +237,7 @@
 
 GCNIterativeScheduler::GCNIterativeScheduler(MachineSchedContext *C,
                                              StrategyKind S)
-  : BaseClass(C, llvm::make_unique<SchedStrategyStub>())
+  : BaseClass(C, std::make_unique<SchedStrategyStub>())
   , Context(C)
   , Strategy(S)
   , UPTracker(*LIS) {