Back-end specific per-bfd data

[Nick Clifton]

Hi Mark,

: There seems to be no place to put back-end specific per-bfd data.
: That means that some of the backends have resulted to static data,
: which is surely not the right thing given the otherwise nicely
: object-oriented and reentrant nature of bfd.

The current method, used by several ports, is to hang the data off
a custom made link hash table.  For examples of this see struct
coff_arm_link_hash_table in coff-arm.c or struct
elf32_mn10300_link_hash_entry in elf-m10300.c

Cheers
	Nick