archbuild: allow passing through the SOURCE_DATE_EPOCH variable

When using restrictive sudoers profiles, the builtin mechanism for
whitelisting this variable on the sudo command line does not work.

Explicitly whitelist it anyway by matching on the ARCHBUILD role.

roles/archbuild/files/sudoers

@@ -3,5 +3,7 @@ Cmnd_Alias ARCHBUILD = /usr/sbin/makechrootpkg, /usr/sbin/mkarchroot, \
                        /usr/sbin/arch-nspawn, /usr/local/bin/syncrepo, /usr/bin/multilib-build, \
                        /usr/bin/multilib-testing-build,    /usr/bin/multilib-staging-build
 
+Defaults!ARCHBUILD     env_keep+=SOURCE_DATE_EPOCH
+
 %dev ALL = NOPASSWD: ARCHBUILD
 %tu  ALL = NOPASSWD: ARCHBUILD