mn10300: relaxing vs section merging

[DJ Delorie]

> It doesn't look right to me.  You are adding irel->r_addend to symval
> where you previously did not.

That's because _bfd_elf_rela_local_sym adjusts the addend according to
where the symbol has been (so far) relocated to.  That's the value we
need for checking relax limits, so we need to add it in.

I don't think "previously" counts here.  It didn't work previously.