gcc: unify cleanup of include-fixed, apply to cross-canadian

gcc: unify cleanup of include-fixed, apply to cross-canadian

Since target and cross variants were already doing similar cleanup
of include-fixed headers, as those aren't used, unify the code and
also apply the same to cross-canadian variant.

Some of those header files get processed with a tool that leaves
absolute buildpaths inside the file's commented section, causing
QA errors. Since those aren't used, let's remove them.

This may be a temporary solution until the tool itself gets fixed
to not embed absolute buildpaths in the header files:
https://lists.openembedded.org/g/openembedded-core/topic/107268307

Signed-off-by: Denys Dmytriyenko <denys@konsulko.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>