[rfc] new bfd hook: additional link map text

[DJ Delorie]

> I think the idea is good.  I'm assuming the previous patch won't be
> going in, nor the debug printfs. :)  The place to declare

Nope :-)

> rx_additional_link_map_text is in a new bfd/elf32-rx.h file, included
> by both ld/emultempl/rxelf.em and bfd/elf32-rx.c, assuming the latter
> is where you'll define the function.

Makes sense.  I don't see any clear rule about what goes in
include/*.h vs bfd/*.h though - and there are some files in include/
which #include headers in bfd/ too :-P