Updated Geant4 and dependencies clhep and vecgeom to use cxxstd= variant (#10518)

* Updated Geant4 and dependencies clhep and vecgeom to use cxxstd= variant so that it is applied consistently.

* Make standalone geant4 data packages that are used when data is not installed with geant4. This allows installing the data files are externals that can be common to many compiler version.

* move geant4 data package dependencies to umbrella package geant4-data

var/spack/repos/builtin/packages/g4realsurface/package.py

@@ -0,0 +1,28 @@
+# 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 *
+import os
+
+
+class G4realsurface(Package):
+    """Geant4 data for measured optical surface reflectance"""
+    homepage = "http://geant4.web.cern.ch"
+    url = "http://geant4-data.web.cern.ch/geant4-data/datasets/RealSurface.1.0.tar.gz"
+
+    version('1.0', '3e2d2506600d2780ed903f1f2681962e208039329347c58ba1916740679020b1')
+    version('2.1', '2a287adbda1c0292571edeae2082a65b7f7bd6cf2bf088432d1d6f889426dcf3')
+    version('2.1.1', '90481ff97a7c3fa792b7a2a21c9ed80a40e6be386e581a39950c844b2dd06f50')
+
+    def install(self, spec, prefix):
+        mkdirp(join_path(prefix.share, 'data'))
+        install_path = join_path(prefix.share, 'data',
+                                 os.path.basename(self.stage.source_path))
+        install_tree(self.stage.source_path, install_path)
+
+    def url_for_version(self, version):
+        """Handle version string."""
+        return ("http://geant4-data.web.cern.ch/geant4-data/datasets/RealSurface.1.0.tar.gz" % version)