stackwalk: derive glibc pointer mangling on ARM
glibc has long protected ARM setjmp stack and return addresses with its process-wide pointer guard, and its new common scheme also rotates them. Treating those entries as raw addresses can therefore make simulated longjmp restore invalid state.
Include ARM's stack-pointer slot in the existing two-probe derivation. This covers both the older XOR-only representation and the current 9-bit rotation without depending on the guard's private location.
Co-authored-by: OpenAI Codex <noreply@openai.com>
