Make llvm::StringRef to std::string conversions explicit.

This is how it should've been and brings it more in line with
std::string_view. There should be no functional change here.

This is mostly mechanical from a custom clang-tidy check, with a lot of
manual fixups. It uncovers a lot of minor inefficiencies.

This doesn't actually modify StringRef yet, I'll do that in a follow-up.

lldb/source/Plugins/LanguageRuntime/RenderScript/RenderScriptRuntime/RenderScriptExpressionOpts.cpp

@@ -86,7 +86,7 @@ bool RenderScriptRuntimeModulePass::runOnModule(llvm::Module &module) {
   llvm::StringRef real_triple =
       m_process_ptr->GetTarget().GetArchitecture().GetTriple().getTriple();
   const llvm::Target *target_info =
-      llvm::TargetRegistry::lookupTarget(real_triple, err);
+      llvm::TargetRegistry::lookupTarget(std::string(real_triple), err);
   if (!target_info) {
     if (log)
       log->Warning("couldn't determine real target architecture: '%s'",