linux-user/aarch64: Implement prctls for GCS This is PR_GET_SHADOW_STACK_STATUS, PR_SET_SHADOW_STACK_STATUS, and PR_LOCK_SHADOW_STACK_STATUS. Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org> Signed-off-by: Richard Henderson <richard.henderson@linaro.org> Message-id: 20251008215613.300150-64-richard.henderson@linaro.org Signed-off-by: Peter Maydell <peter.maydell@linaro.org>