Explicitly convert StringRef to std::string for compatibility with libstdc++ 5.4.0

For some reason, the user-defined implicit conversion from StringRef to
std::string is not invoked by std::map::emplace in libstdc++ 5.4.0, even
though it works fine on modern systems.

Author: gribozavr

llvm/lib/ProfileData/SampleProf.cpp

@@ -521,7 +521,7 @@ void CSProfileConverter::convertProfiles(CSProfileConverter::FrameNode &Node) {
     if (NodeProfile) {
       // Add child profile to the callsite profile map.
       auto &SamplesMap = NodeProfile->functionSamplesAt(ChildNode.CallSiteLoc);
-      SamplesMap.emplace(OrigChildContext.getName(), *ChildProfile);
+      SamplesMap.emplace(OrigChildContext.getName().str(), *ChildProfile);
       NodeProfile->addTotalSamples(ChildProfile->getTotalSamples());
     }