RFC: Unify overflow checking

[Nick Clifton]

Hi Daniel,

> Does anyone remember why bfd_check_overflow and _bfd_relocate_contents
> have different overflow checks? 

Well bfd_relocate_contents has to deal with whatever is the location 
being relocated whereas bfd_check_overflow just has to examine an 
already relocated value.

 > It looks to me as if the ones in
 > _bfd_relocate_contents are always appropriate, and bfd_check_overflow
 > is simply stale.

I agree that this is probably true, so some code simplification would be 
welcome.

>  This (untested so far) patch unifies them. 

It does not work either.    (For example it tests a variable called 'x' 
which has not been defined).  It is the right general idea though, 
should you feel like cleaning it up and testing it.

Cheers
   Nick