Patch: add gc-sections warning and H8 support

[Grant Edwards]

> > The attached patch adds gc-sections support for the H8 target
> > and adds a warning (for all targets) if the gc-sections option
> > is ignored.
> 
> Applied with a few tweaks.  I replaced your multiple elf_gc_sections
> warnings with just one warning, because I think giving reasons for a
> warning belongs in an info file rather than the executable.

Cool. That's what I started out with.  I split it up to make
sure I understood what was going on, and then I just left that
way.

-- 
Grant Edwards
grante@visi.com