Revert "Convert a few std::strings to StringRef."

This reverts commit r212342.

We can get a StringRef into the current Record, but not one in the bitcode
itself since the string is compressed in it.

llvm-svn: 212356
diff --git a/llvm/lib/LTO/LTOModule.cpp b/llvm/lib/LTO/LTOModule.cpp
index 2fa450f..5b3057177 100644
--- a/llvm/lib/LTO/LTOModule.cpp
+++ b/llvm/lib/LTO/LTOModule.cpp
@@ -63,8 +63,8 @@
 
 bool LTOModule::isBitcodeForTarget(MemoryBuffer *buffer,
                                    StringRef triplePrefix) {
-  StringRef Triple = getBitcodeTargetTriple(buffer, getGlobalContext());
-  return Triple.startswith(triplePrefix);
+  std::string Triple = getBitcodeTargetTriple(buffer, getGlobalContext());
+  return StringRef(Triple).startswith(triplePrefix);
 }
 
 LTOModule *LTOModule::createFromFile(const char *path, TargetOptions options,