llvm/tools/llvm-cgdata/llvm-cgdata.cpp:69: 2 * clumsy string parameter passing

[dcb314]

Static analyser cppcheck says:

trunk/llvm/tools/llvm-cgdata/llvm-cgdata.cpp:69:39: performance: Function parameter 'Hint' should be passed by const reference. [passedByValue]
trunk/llvm/tools/llvm-cgdata/llvm-cgdata.cpp:68:54: performance: Function parameter 'Whence' should be passed by const reference. [passedByValue]

Source code is

static void exitWithError(Twine Message, std::string Whence = "",
std::string Hint = "") {