sourceware.org: mirror urls (#15992)

sourceware.org is often quite overrun and times out or results in
certificate errors.

Since libffi, bzip2, elfutils, etc. are quite fundamental in
build chains, lets add some official mirrors.

libffi, bzip2, elfutils, lvm2, valgrind: add mirrors

lib/spack/spack/build_systems/sourceware.py

@@ -0,0 +1,37 @@
+# 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)
+
+import spack.util.url
+import spack.package
+
+
+class SourcewarePackage(spack.package.PackageBase):
+    """Mixin that takes care of setting url and mirrors for Sourceware.org
+       packages."""
+    #: Path of the package in a Sourceware mirror
+    sourceware_mirror_path = None
+
+    #: List of Sourceware mirrors used by Spack
+    base_mirrors = [
+        'https://sourceware.org/pub/',
+        'https://mirrors.kernel.org/sourceware/',
+        'https://ftp.gwdg.de/pub/linux/sources.redhat.com/'
+    ]
+
+    @property
+    def urls(self):
+        self._ensure_sourceware_mirror_path_is_set_or_raise()
+        return [
+            spack.util.url.join(m, self.sourceware_mirror_path,
+                                resolve_href=True)
+            for m in self.base_mirrors
+        ]
+
+    def _ensure_sourceware_mirror_path_is_set_or_raise(self):
+        if self.sourceware_mirror_path is None:
+            cls_name = type(self).__name__
+            msg = ('{0} must define a `sourceware_mirror_path` attribute'
+                   ' [none defined]')
+            raise AttributeError(msg.format(cls_name))

lib/spack/spack/pkgkit.py

@@ -31,6 +31,7 @@
 from spack.build_systems.meson import MesonPackage
 from spack.build_systems.sip import SIPPackage
 from spack.build_systems.gnu import GNUMirrorPackage
+from spack.build_systems.sourceware import SourcewarePackage
 
 from spack.mixins import filter_compiler_wrappers