asm_trampoline.S misses GCS flag for aarch64

[ggardet]

Bug report

Bug description:

When building with GCC15+, binutils 2.44+, glibc 2.41+ and -mbranch-protection=standard on aarch64, this enables PAC and BTI as stated in #139808 but also GCS (Guarded Control Stack).
PAC/BTI is already covered with #130864
For GCS, we would need to add some additional gnu properties on top of this patch, similarly to smuellerDD/leancrypto@fe9751f

Maybe #130864 could be updated to also cover GCS?

More details on GCS:

• https://community.arm.com/arm-community-blogs/b/tools-software-ides-blog/posts/gcc-15-continuously-improving#guarded
• https://docs.kernel.org/next/arch/arm64/gcs.html

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux