Archive all patches in a package after install (#12653)

When Spack installs a package it writes the package.py file and
patches to a separate repository (which reflects the state of the
package at the time it was installed). Previously, Spack only wrote
patches that were used at installation time. This updates the
archiving step to include all patch files that are relevant to the
package (in case that repository is used in another context).

lib/spack/spack/repo.py

@@ -9,6 +9,7 @@
 import errno
 import functools
 import inspect
+import itertools
 import os
 import re
 import shutil
@@ -921,7 +922,9 @@ def dump_provenance(self, spec, path):
 
         # Install patch files needed by the package.
         mkdirp(path)
-        for patch in spec.patches:
+        for patch in itertools.chain.from_iterable(
+                spec.package.patches.values()):
+
             if patch.path:
                 if os.path.exists(patch.path):
                     install(patch.path, path)