Strip authentication bits from vtable load address (#71128)

The current Darwin arm64e ABI on AArch64 systems using ARMv8.3 & newer
cores, adds authentication bits to the vtable pointer address. The
vtable address must be in addressable memory, so running it through
Process::FixDataAddress will be a no-op on other targets.

This was originally a downstream change that I hadn't upstreamed yet,
and it was surfaced by Greg's changes in
https://github.com/llvm/llvm-project/pull/67599
so I needed to update the local patch, and was reminded that I should
upstream this.