[committed] Add a MIPS -mfix-vr4130 option

[Richard Sandiford]

Mark Mitchell <mark@codesourcery.com> writes:
> (If GAS is adding NOPs, then, in order to be really correct, you need to
> modify the length estimates used by the compiler, or we'll start getting
> out-of-range branch instructions in the compiler.)

It's generally accepted (I think!) that this sort of assembly munging
can lead to out-of-range branches, both in compiler-generated code and
hand-written code.  That's one of the reasons why the assembler supports
branch relaxation.  I.e., if you use -mfix-vr4130 and get out-of-range
branches, the correct thing to do is add -Wa,-relax-branch.

> I think whether or not to apply this to 4.0 is something that you can
> decided in your capacity as the target maintainer.

OK, thanks, I've applied it.  I didn't know how much leeway we
target maintainers had.

Richard