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

Bắt đầu với asm_trampoline.S và phần xử lý PAC/BTI hiện có từ pull request 130864. So sánh các thuộc tính GNU trong commit leancrypto được tham chiếu, sau đó build CPython main trên Linux với GCC 15+, binutils 2.44+, glibc 2.41+ và -mbranch-protection=standard; hoàn tất nghĩa là trampoline aarch64 cũng khai báo hỗ trợ GCS.