Make the hashing algorithm Endian neutral. This is a bit annoying, but

folks who know something about PPC tell me that the byte swap is crazy
fast and without this the bit mixture would actually be different. It
might not be worse, but I've not measured it and so I'd rather not trust
it. This way, the algorithm is identical on both endianness hosts. I'll
look into any performance issues etc stemming from this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151892 91177308-0d34-0410-b5e6-96231b3b80d8