LoongArch: Disable executable stack by default

Disable executable stack for LoongArch by default, as all modern
architectures do.

Reported-by: Andreas Schwab <schwab@suse.de>
Suggested-by: WANG Xuerui <git@xen0n.name>
Link: https://sourceware.org/pipermail/binutils/2022-July/121992.html


Tested-by: WANG Xuerui <git@xen0n.name>
Tested-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>