asm_trampoline.S misses GCS flag for aarch64

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 https://github.com/python/cpython/issues/139808 but also GCS (Guarded Control Stack).
PAC/BTI is already covered with https://github.com/python/cpython/pull/130864
For GCS, we would need to add some additional gnu properties on top of this patch, similarly to https://github.com/smuellerDD/leancrypto/commit/fe9751f2b13581e938f25b82f3e725372223af81

Maybe https://github.com/python/cpython/pull/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

Commencez par asm_trampoline.S et la gestion existante de PAC/BTI issue de la pull request 130864. Comparez les propriétés GNU du commit leancrypto référencé, puis construisez CPython main sous Linux avec GCC 15+, binutils 2.44+, glibc 2.41+ et -mbranch-protection=standard ; la tâche est terminée lorsque le trampoline aarch64 déclare également la prise en charge de GCS.