debugging: handle alternate signal stacks better on RISCV
debugging: handle alternate signal stacks better on RISCV

In the case that we are unwinding with context, if the retreived frame pointer
matches the signal context, assume that the value is valid and do not perform
confidence checks.  In any other case, continue to perform some validation to
avoid returning an incorrect frame pointer.

Given that the VDSO path is currently untested, remove the code to simplify the
logic in the frame walking.

PiperOrigin-RevId: 465360612
Change-Id: Iac656012182a12814bafecf20225ba68b90b4db1

abseil/abseil-cpp,abseil/abseil-cpp,abseil/abseil-cpp,abseil/abseil-cpp