[libunwind] [libunwind] Add GCS support for AArch64 (PR #99335)

[John Brawn via cfe-commits]

john-brawn-arm wrote:

> Looks like this breaks building on Android: https://ci.chromium.org/ui/p/chromium/builders/try/android-arm64-rel/680348/overview

Looks like Android here is being built with clang-llvmorg-19-init-14561-gecea8371-3004.tar.xz which looks like it's built from commit https://github.com/llvm/llvm-project/commit/ecea8371 which is after https://github.com/llvm/llvm-project/commit/40d5c2b (which made `-mbranch-protection=standard` enable GCS) but before 3a14ffbae (which added GCS intrinsics to arm_acle.h).

https://github.com/llvm/llvm-project/pull/99335