submodule.c: use argv_array in is_submodule_modified

struct argv_array is easier to use and maintain.
Signed-off-by: NStefan Beller <sbeller@google.com>
Reviewed-by: NJonathan Nieder <jrnieder@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

submodule.c

@@ -1043,12 +1043,6 @@ unsigned is_submodule_modified(const char *path, int ignore_untracked)
 {
 	ssize_t len;
 	struct child_process cp = CHILD_PROCESS_INIT;
-	const char *argv[] = {
-		"status",
-		"--porcelain",
-		NULL,
-		NULL,
-	};
 	struct strbuf buf = STRBUF_INIT;
 	unsigned dirty_submodule = 0;
 	const char *line, *next_line;
@@ -1066,10 +1060,10 @@ unsigned is_submodule_modified(const char *path, int ignore_untracked)
 	}
 	strbuf_reset(&buf);
 
+	argv_array_pushl(&cp.args, "status", "--porcelain", NULL);
 	if (ignore_untracked)
-		argv[2] = "-uno";
+		argv_array_push(&cp.args, "-uno");
 
-	cp.argv = argv;
 	prepare_submodule_repo_env(&cp.env_array);
 	cp.git_cmd = 1;
 	cp.no_stdin = 1;