Using murmurhash2 instead of fnv

[Davide Italiano via llvm-commits]

On Fri, Sep 9, 2016 at 7:03 AM, Rafael Espíndola via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> One annoying property of fnv is that it does one multiplication per
> byte. Murmurhash2 does 3 per every 8 bytes.
>
> With the attached hack linking libxul.so goes from 7.496263743s to 6.661119354.
>
> If there is no objections I will write a proper patch for it.
>

I think this is a good idea but I'd recommend to try on multiple
testcases if you have a time.

-- 
Davide

"There are no solved problems; there are only problems that are more
or less solved" -- Henri Poincare