devel/xxhash: new port
xxHash is an extremely fast non-cryptographic hash algorithm, running at RAM
speed limits. It is proposed in two flavors, 32 and 64 bits. It successfully
completes the SMHasher test suite which evaluates collision, dispersion and
randomness qualities of hash functions. Code is highly portable, and hashes
are identical on all platforms (little / big endian).
Approved by: feld (mentor)
Differential Revision: https://reviews.freebsd.org/D9468