[Bug other/118223] Improve autodependency generation to avoid full product build

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118223

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC itself has auto-generated headers and are handled just fine in its
makefile.