builtin/gc: move rerere garbage collection into separate function

In a subsequent commit we are going to introduce a new "rerere-gc" task
for git-maintenance(1). To prepare for this, refactor the code that
spawns `git rerere gc` into a separate function.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

builtin/gc.c

@@ -384,6 +384,15 @@ static int worktree_prune_condition(struct gc_config *cfg)
 	return should_prune;
 }
 
+static int maintenance_task_rerere_gc(struct maintenance_run_opts *opts UNUSED,
+				      struct gc_config *cfg UNUSED)
+{
+	struct child_process rerere_cmd = CHILD_PROCESS_INIT;
+	rerere_cmd.git_cmd = 1;
+	strvec_pushl(&rerere_cmd.args, "rerere", "gc", NULL);
+	return run_command(&rerere_cmd);
+}
+
 static int too_many_loose_objects(struct gc_config *cfg)
 {
 	/*
@@ -785,7 +794,6 @@ int cmd_gc(int argc,
 	int daemonized = 0;
 	int keep_largest_pack = -1;
 	timestamp_t dummy;
-	struct child_process rerere_cmd = CHILD_PROCESS_INIT;
 	struct maintenance_run_opts opts = MAINTENANCE_RUN_OPTS_INIT;
 	struct gc_config cfg = GC_CONFIG_INIT;
 	const char *prune_expire_sentinel = "sentinel";
@@ -968,10 +976,8 @@ int cmd_gc(int argc,
 	    maintenance_task_worktree_prune(&opts, &cfg))
 		die(FAILED_RUN, "worktree");
 
-	rerere_cmd.git_cmd = 1;
-	strvec_pushl(&rerere_cmd.args, "rerere", "gc", NULL);
-	if (run_command(&rerere_cmd))
-		die(FAILED_RUN, rerere_cmd.args.v[0]);
+	if (maintenance_task_rerere_gc(&opts, &cfg))
+		die(FAILED_RUN, "rerere");
 
 	report_garbage = report_pack_garbage;
 	reprepare_packed_git(the_repository);