TARGET_MINSIGSTKSZ has been defined in generic/signal.h
or target_signal.h, We don't need to define it again.

Signed-off-by: Song Gao <gaosong@loongson.cn>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <1637893388-10282-3-git-send-email-gaosong@loongson.cn>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>