TARGET_SIGSTKSZ is not used, we should remove it.

Signed-off-by: Song Gao <gaosong@loongson.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <1637893388-10282-4-git-send-email-gaosong@loongson.cn>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>