[PATCH] Handle llvm::Triple::GNU and llvm::Triple::Hurd in several places.

[Rafael Espíndola]

> +  // Don't use a frame pointer on GNU/Linux and GNU/Hurd x86 and x86_64 if
> +  // optimizing.

This is really just the OS, so just linux and hurd I guess.

The patch also needs tests.

Thanks,
Rafael