Convert a few std::strings to StringRef.

llvm-svn: 212342
diff --git a/llvm/lib/LTO/LTOModule.cpp b/llvm/lib/LTO/LTOModule.cpp
index 961c759..589ce2d 100644
--- a/llvm/lib/LTO/LTOModule.cpp
+++ b/llvm/lib/LTO/LTOModule.cpp
@@ -70,8 +70,8 @@
 
 bool LTOModule::isBitcodeForTarget(MemoryBuffer *buffer,
                                    StringRef triplePrefix) {
-  std::string Triple = getBitcodeTargetTriple(buffer, getGlobalContext());
-  return StringRef(Triple).startswith(triplePrefix);
+  StringRef Triple = getBitcodeTargetTriple(buffer, getGlobalContext());
+  return Triple.startswith(triplePrefix);
 }
 
 LTOModule *LTOModule::createFromFile(const char *path, TargetOptions options,