[LLVMdev] Correct use of StringRef and Twine

[David Blaikie]

>> Perhaps, I suppose, I'm not sure just how portable llvm code is.
>
> Very portable AFAICT. I'm even going to port it to my hobbyist OS once C++
> rtti is totally gone in the llvm code base.

Sorry, I meant source portable to different compilers (ie: which
compilers does llvm compile on & how many have really poor std::string
implementations).

- David