ARM BE8 linker support

[Richard Earnshaw]

Paul,

I've just realized that there are a couple of omissions from this patch 
(there's no need to back it out, but I think they would be best addressed 
while the patch is fresh in your mind):

BE8 mode should really only be possible for EABI v3 or later images.

It ought to be possible to create a configuration where BE8 mode is the 
default (assuming a big-endian object file)...

...so it should also be possible to disable that behaviour by requesting a 
BE32 image.

I'm not sure if this can happen, but it shouldn't be possible to generate 
BE8 when doing a partial link.

R.