Update xxhash to r37.
Use XXH64 on 64-bit systems.

I'm not able to reproduce any real performance difference, but I know
there are some games which do more hashing and it may help there.
Merge pull request #7028 from unknownbrackets/xxhash-update

Update xxHash to r37, including XXH64
Rebase RadarNyan work on Generate version while build on Wiondows
Merge branch 'windows-exe-version' of https://github.com/RadarNyan/ppsspp into verbuild

Conflicts:
	Windows/version.rc