Add new package: re2 (#18302)

* Add new package: re2

* re2: refine versions

var/spack/repos/builtin/packages/re2/package.py

@@ -0,0 +1,17 @@
+# Copyright 2013-2020 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack import *
+
+
+class Re2(CMakePackage):
+    """RE2 is a fast, safe, thread-friendly alternative to backtracking
+    regular expression engines like those used in PCRE, Perl, and Python."""
+
+    homepage = "https://github.com/google/re2"
+    url      = "https://github.com/google/re2/archive/2020-08-01.tar.gz"
+
+    version('2020-08-01', sha256='6f4c8514249cd65b9e85d3e6f4c35595809a63ad71c5d93083e4d1dcdf9e0cd6')
+    version('2020-04-01', sha256='98794bc5416326817498384a9c43cbb5a406bab8da9f84f83c39ecad43ed5cea')