[runtimes][PAC] Harden unwinding when possible (#143230)

This hardens the unwinding logic and datastructures on systems
that support pointer authentication.

The approach taken to hardening is to harden the schemas of as many
high value fields in the myriad structs as possible, and then also
explicitly qualify local variables referencing privileged or security
critical values.

This does introduce ABI linkage between libcxx, libcxxabi, and
libunwind but those are in principle separate from the OS itself
so we've kept the schema definitions in the library specific headers
rather than ptrauth.h

0 files changed, 0 insertions, 0 deletions