New package xxhash. (#8530)

* New package xxhash.

* Change requested by @adamjstewart.

var/spack/repos/builtin/packages/xxhash/package.py

+##############################################################################
+# Copyright (c) 2013-2018, Lawrence Livermore National Security, LLC.
+# Produced at the Lawrence Livermore National Laboratory.
+#
+# This file is part of Spack.
+# Created by Todd Gamblin, tgamblin@llnl.gov, All rights reserved.
+# LLNL-CODE-647188
+#
+# For details, see https://github.com/spack/spack
+# Please also see the NOTICE and LICENSE files for our notice and the LGPL.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License (as
+# published by the Free Software Foundation) version 2.1, February 1999.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the IMPLIED WARRANTY OF
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the terms and
+# conditions of the GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+##############################################################################
+from spack import *
+
+
+class Xxhash(MakefilePackage):
+    """xxHash is an Extremely fast Hash algorithm, running at RAM speed
+    limits. 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).
+    """
+
+    homepage = "https://github.com/Cyan4973/xxHash"
+    url      = "https://github.com/Cyan4973/xxHash/archive/v0.6.5.tar.gz"
+
+    version('0.6.5', '6af3a964f3c2accebce66e54b44b6446')
+    version('0.6.4', '3c071c95e31bd601cca149cc354e6f19')
+    version('0.6.3', 'f2ec1497317c0eb89addd7f333c83228')
+    version('0.6.2', 'b2d12d99094b824e0a5f3ab63abc6c58')
+    version('0.6.1', 'f4ced3767aad8384b1ecb73bd5f992ca')
+    version('0.6.0', 'e0fd163b07ab0038f389a180dc263cf2')
+    version('0.5.1', '9417fd8a4d88204b680e21a60f0ccada')
+    version('0.5.0', '42e9a31a2cfc2f626fde17e84a0b6bb7')
+
+    def install(self, spec, prefix):
+        make('prefix={0}'.format(prefix), 'install')