Porting BFD to new architecture

[ibanez@sunplus.com]

 We are porting libbfd to a new architecture.
 But the libbfd internal is highly architecture dependent which
 is very different with other tools.

 For example, to port gas to a new target, all we need to do
 is add some target related files, add a few lines to the config file
 and rebuild it.

 But to port bfd, we need to hack the bfd source code.
 It makes upgrade to a new libbfd version impossible without re-porting.

 How can we add our architecture to the libbfd in a smart and transparent
way?