Using murmurhash2 instead of fnv

[Ed Maste via llvm-commits]

On 9 September 2016 at 15:09, Davide Italiano via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
>
> 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.

It might be interesting to compare with xxHash too.