completion: use __gitcomp_builtin in _git_gc

The new completable option is --quiet.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/gc.c b/builtin/gc.c
index 3c5eae0..7fc5c16 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -360,8 +360,11 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 			N_("prune unreferenced objects"),
 			PARSE_OPT_OPTARG, NULL, (intptr_t)prune_expire },
 		OPT_BOOL(0, "aggressive", &aggressive, N_("be more thorough (increased runtime)")),
-		OPT_BOOL(0, "auto", &auto_gc, N_("enable auto-gc mode")),
-		OPT_BOOL(0, "force", &force, N_("force running gc even if there may be another gc running")),
+		OPT_BOOL_F(0, "auto", &auto_gc, N_("enable auto-gc mode"),
+			   PARSE_OPT_NOCOMPLETE),
+		OPT_BOOL_F(0, "force", &force,
+			   N_("force running gc even if there may be another gc running"),
+			   PARSE_OPT_NOCOMPLETE),
 		OPT_END()
 	};