Bug#200003: cpp: contains non-free manpages
FYI, the reason those manpages exist in the first place, is that the
GCC Texinfo manual is under the GFDL, and the manpages cpp.1/gcc.1 are
automatically generated from it. The FSF advised us (the GCC
maintainers) that creating and distributing separate manpages for each
of the Invariant Sections was an acceptable alternative to embedding
the full text of the Invariant Sections in each manpage.
I'd suggest you deal with this as an instance of the general GFDL