No Fortran

[Joe Buck]

> I'm still not entirely sure that we should avoid building libg2c
> even when `f77' is not in the list of languages.  Do we avoid
> building the C++ libraries when "c++" isn't in that list?

Yes.  We have to, since the C++ libraries are mostly written in C++
and we don't assume the user has a C++ compiler if we didn't just
build one.

Furthermore, even if we didn't, we shouldn't waste users' time
building stuff when they thought they asked to exclude it.