Silence an "illegal conversion" diagnostic

MSVC was issuing "illegal conversion; more than one user-defined
conversion has been implicitly applied" as a warning on this code.
Explicitly calling .str() causes a StringRef to be materialized so
that a second user-defined conversion is not required.

clang-tools-extra/clangd/CompileCommands.cpp

@@ -48,7 +48,7 @@ llvm::Optional<std::string> queryXcrun(llvm::ArrayRef<llvm::StringRef> Argv) {
   llvm::sys::fs::createTemporaryFile("clangd-xcrun", "", OutFile);
   llvm::FileRemover OutRemover(OutFile);
   llvm::Optional<llvm::StringRef> Redirects[3] = {
-      /*stdin=*/{""}, /*stdout=*/{OutFile}, /*stderr=*/{""}};
+      /*stdin=*/{""}, /*stdout=*/{OutFile.str()}, /*stderr=*/{""}};
   vlog("Invoking {0} to find clang installation", *Xcrun);
   int Ret = llvm::sys::ExecuteAndWait(*Xcrun, Argv,
                                       /*Env=*/llvm::None, Redirects,