message: Fix use-after-free in CommandCompletions.cpp
  The code was creating a StringRef to a temporary std::string. The
  solution is to just drop the .str() from the original StringRef.
  This manifested it self as the new TestCompletions test failing in some
  configurations.
diff: @@ -164,7 +164,7 @@ static int DiskFilesOrDirectories(const llvm::Twine &partial_name,
  // search in the fully resolved directory, but CompletionBuffer keeps the
  // unmodified form that the user typed.
  Storage = Resolved;
  - llvm::StringRef RemainderDir = path::parent_path(Remainder.str());
  + llvm::StringRef RemainderDir = path::parent_path(Remainder);
  if (!RemainderDir.empty()) {
  // Append the remaining path to the resolved directory.
  Storage.append(path::get_separator());
  