[C++11] Replace llvm::tie with std::tie.

The old implementation is no longer needed in C++11.

llvm-svn: 202644
diff --git a/llvm/lib/CodeGen/MachineTraceMetrics.cpp b/llvm/lib/CodeGen/MachineTraceMetrics.cpp
index 6aa3f67..41cf1ea 100644
--- a/llvm/lib/CodeGen/MachineTraceMetrics.cpp
+++ b/llvm/lib/CodeGen/MachineTraceMetrics.cpp
@@ -944,7 +944,7 @@
   // Update Heights[DefMI] to be the maximum height seen.
   MIHeightMap::iterator I;
   bool New;
-  tie(I, New) = Heights.insert(std::make_pair(Dep.DefMI, UseHeight));
+  std::tie(I, New) = Heights.insert(std::make_pair(Dep.DefMI, UseHeight));
   if (New)
     return true;