Gaudi package: new version + xenv bugfix (#10668)

Extract implicit xenv dependency into a new package and add it as an
explicit dependency. Update Gaudi to explicitly depend on older
versions of xenv rather than the latest develop because that
conflicts with Spack's compiler wrappers.

var/spack/repos/builtin/packages/py-xenv/package.py

@@ -0,0 +1,21 @@
+# Copyright 2013-2019 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 PyXenv(PythonPackage):
+    """Helpers to work with the environment in a platform independent way."""
+
+    homepage = "https://gitlab.cern.ch/gaudi/xenv"
+    git      = "https://gitlab.cern.ch/gaudi/xenv.git"
+
+    # As of 0.0.4, all released versions of xenv corrupt the system environment
+    # in a manner which breaks Spack's compiler wrappers. Therefore, we must
+    # package an un-released development version of xenv.
+    version('develop',            branch='master')
+    version('develop_2018-12-20', commit='ddc3bf5e65e1689da499f639af7a27c5c4242841')
+
+    depends_on('py-setuptools', type='build')