More CA derivations prep

Again, with care not to change the schema in any way.

src/script/hydra-eval-jobset

@@ -438,13 +438,17 @@ sub checkBuild {
         # new build to be scheduled if the meta.maintainers field is
         # changed?
         if (defined $prevEval) {
+            my $pathOrDrvConstraint = defined $firstOutputPath
+                ? { path => $firstOutputPath }
+                : { drvPath => $drvPath };
+
             my ($prevBuild) = $prevEval->builds->search(
                 # The "project" and "jobset" constraints are
                 # semantically unnecessary (because they're implied by
                 # the eval), but they give a factor 1000 speedup on
                 # the Nixpkgs jobset with PostgreSQL.
                 { jobset_id => $jobset->get_column('id'), job => $jobName,
-                  name => $firstOutputName, path => $firstOutputPath },
+                  name => $firstOutputName, %$pathOrDrvConstraint },
                 { rows => 1, columns => ['id', 'finished'], join => ['buildoutputs'] });
             if (defined $prevBuild) {
                 #print STDERR "    already scheduled/built as build ", $prevBuild->id, "\n";