lhapdf5: new package at v5.9.1 (#17746)

During configure lhapdf5 searches for python. On one system
I tested on (ubuntu 19.10) it finds a system installed python3
and fails to create the python extension.

Variant named to make explicit that this is only a python2 extension.

var/spack/repos/builtin/packages/lhapdf5/package.py

@@ -0,0 +1,46 @@
+# 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 Lhapdf5(AutotoolsPackage):
+    """LHAPDF is a general purpose Fortran 77/90 interpolator,
+    used for evaluating PDFs from discretised data files."""
+
+    homepage = "http://lhapdf.hepforge.org/lhapdf5/"
+    url      = "http://lhapdf.hepforge.org/downloads?f=old/lhapdf-5.9.1.tar.gz"
+
+    version('5.9.1', sha256='86b9b046d7f25627ce2aab6847ef1c5534972f4bae18de98225080cf5086919c')
+    version('5.9.0', sha256='64b9018ce6102ae7b6a92c990ca6afa841fb992d87b1abf5756c3d04c4d46b9c')
+    version('5.8.9', sha256='b90a83512fc5f51e4cd419f1e79ad6e6fcd0e19636bb07464e41f47ee0509d3c')
+    version('5.8.8', sha256='fe4c7148b1858c3c534c5e80ea1a8766b4407d19c44c40578da54e390af228f8')
+    version('5.8.7', sha256='4c6effdcc74c8b60aaa18bf60e224de3c5f3c2e5b0efc08d38338f01bec7db47')
+    version('5.8.6', sha256='689800b2ad6d822e2da0435f9303457feaa9102bff8ef9dbfd708e13afceeef2')
+    version('5.8.5', sha256='f37d87c70a65a770bb2d013c4d1d9aa5d90c0f52b9430d56bab578fd221e8e41')
+    version('5.8.4', sha256='75a3b44bd4509bec47806fb5ad4baaa6334a2aa8f51cf2f7195d4f08bd353ca2')
+    version('5.8.3', sha256='e9b5e72bab65adef9ef78a5e0ee526a6ee673bed142f5e3617c0a27029b84275')
+    version('5.8.2', sha256='c54b4153b43453426510fd8aa322de66a80a33137ad251124345309615f6a3a6')
+    version('5.8.1', sha256='e113818541e976be69a9524007c2db19059da9af7abfebf7c53d86eafa2109c9')
+    version('5.8.0', sha256='8381ea5f785dde95772a2b6d5890f1cb72012e223e6861823fd81b09eedaa7a3')
+    version('5.7.1', sha256='40529629351598317fbf7b5905661e51b23778019d50451eee78d7b1118e2559')
+
+    variant('python2', default=False,
+            description="Enable Python2 extension")
+
+    depends_on('python@2.3:2.7.99', when='+python2')
+
+    def setup_build_environment(self, env):
+        env.append_flags('FFLAGS', '-std=legacy')
+        if self.spec.satisfies('+python2'):
+            env.append_flags(
+                'PYTHON',
+                join_path(self.spec['python'].prefix.bin, 'python'))
+
+    def configure_args(self):
+        args = []
+        if self.spec.satisfies('-python2'):
+            args.append('--disable-pyext')
+        return args