See:
  https://github.com/torvalds/linux/blob/master/arch/loongarch/kernel/signal.c



The kernel setup_sigcontext() set end context size 0.

Signed-off-by: Song Gao <gaosong@loongson.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20231101030816.2353416-4-gaosong@loongson.cn>