Add -mno-branch-likely for mips

[Mike Stump]

> To: Mike Stump <mrs@windriver.com>
> From: Jeffrey A Law <law@redhat.com>
> Date: Fri, 26 Jan 2001 11:45:09 -0700

>   > Add -mno-branch-likely for mips.
>
> So why do you really need this?

Here is what our developer said:

> I think keeping it a separate control would be best.

> The branch-likely instructions work well for some processor
> implementations, but extremely poorly for others (basically, it
> defeats dynamic branch prediction logic).  It's not particularly
> tied to the MIPS ISA level.  We use it as the default for some
> libraries, based on the actual silicon we want to target with the
> best performance.  But again, it's not always going to be consistant
> wrt. MIPS ISA level.

I've suggested implementing support for the CPU variants he has in
mind, and having them select the likely win by cpu type.  I'll see
what we says to that.

If the above is convincing enough to ok it, let me know.