Some pd externals like pdp (not yet in Portage) needs pd's headers. Right now I do it like this: insinto /usr/include/pd doins m_imp.h g_canvas.h t_tk.h At least, for media-sound/pd-0.39_p1 and _p2.
s_stuff.h is also needed.
And g_all_guis.h
I'm not sure if it will be necessary. On pd-overlay we're trying to make a pd (and pd-extended) build system that makes sense. So, all people who are interested in this bug is encouraged to try and collaborate on http://pd-overlay.sf.net/.