[patch] Factor common code for C-family and Fortran preprocessing (3rd try)

[Tobias Burnus]

  Joseph S. Myers wrote:
> On Fri, 1 Oct 2010, FX wrote
>> Bootstrapped and regtested on x86_64-darwin. OK to commit?
> The C changes are OK.

The Fortran changes are also OK.

Thanks for the patch!

Tobias