cpplib: Separate out translation phases 1 and 2

[Neil Booth]

Devang Patel wrote:-

> I meant, If I were you....
> 
> As a CPP maintainer, I thought, you would ask me to do the same,
> if I ever post big patch!

Nah, I'd say "It looks good, provides a roadmap for implementing multibyte
char support that we don't have, cleans up the code base, and should be
able to make-up for any slowdown with future optimizations it enables.
Put it in!"  8-)

Neil.