heirloom-devtools: Add -fpermissive to C++ flags.

heirloom-devtools: Add -fpermissive to C++ flags.

Seems this doesn't build with newer G++ due to some pointer shenanigans,
I don't really care that much so let's just treat the symptom instead of
the underlying condition.

The -fpermissive flag seems to be an accepted option of G++ since ancient
history.  We'll just add it unconditionally, and now the package installs
successfully.