Add spack build package for Xerces-C which is a supporting package for the krell related projects.

var/spack/packages/xerces-c/package.py

@@ -0,0 +1,36 @@
+# FIXME:
+# This is a template package file for Spack.  We've conveniently
+# put "FIXME" labels next to all the things you'll want to change.
+#
+# Once you've edited all the FIXME's, delete this whole message,
+# save this file, and test out your package like this:
+#
+#     spack install xerces-c
+#
+# You can always get back here to change things with:
+#
+#     spack edit xerces-c
+#
+# See the spack documentation for more information on building
+# packages.
+#
+from spack import *
+
+class XercesC(Package):
+    """ Xerces-C++ is a validating XML parser written in a portable subset of C++.
+    Xerces-C++ makes it easy to give your application the ability to read and
+    write XML data. A shared library is provided for parsing, generating,
+    manipulating, and validating XML documents using the DOM, SAX, and SAX2 APIs.
+    """
+
+    homepage = "https://xerces.apache.org/xerces-c"
+    url      = "https://www.apache.org/dist/xerces/c/3/sources/xerces-c-3.1.2.tar.gz"
+    version('3.1.2', '9eb1048939e88d6a7232c67569b23985')
+
+    def install(self, spec, prefix):
+        configure("--prefix=%s" % prefix,
+                  "--disable-network")
+        make("clean")
+        make()
+        make("install")
+