Add a new package: Metall (#14903)

* Add a new package: Metall

* Fix errors in metall/package.py

* Update var/spack/repos/builtin/packages/metall/package.py

Change to https style URL

Co-Authored-By: Adam J. Stewart <ajstewart426@gmail.com>

* Update in metall/package.py. Change Metall to depend on Boost always

* Update in metall/package.py. Change to install Boost with the default variants

* Update metall/package.py. Removed a comment

Co-authored-by: Adam J. Stewart <ajstewart426@gmail.com>

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

@@ -0,0 +1,22 @@
+# 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)
+
+
+class Metall(CMakePackage):
+    """An allocator for persistent memory"""
+
+    homepage = "https://github.com/LLNL/metall"
+    git      = "https://github.com/LLNL/metall.git"
+
+    maintainers = ['KIwabuchi', 'rogerpearce', 'mayagokhale']
+
+    version('develop', branch='develop')
+
+    depends_on('boost@1.64:', type=('build', 'link'))
+
+    def cmake_args(self):
+        args = []
+        args.append('-DINSTALL_HEADER_ONLY=ON')
+        return args