Delegate to ABI plugin to check if call frame addresses are valid

[pveras]

Specially when dealing with different address spaces, CFAs could start from addresses like 0. ABIs could already specify what they consider to be valid CFA values but this was never used in these parts of the unwinder code. Note that this COULD be a breaking change for ABISysV_arc and ABISysV_riscv since these are the only two ABIs that don't explicitly disallow 0 values.

[walter-erquinigo]

Do you think you can upstream this change?

[pveras]

I can try. Should I just submit a PR upstream? I'll check if upstream has any additional requirements

[walter-erquinigo]

Yeah, resubmit the PR upstream. They'll likely ask for a unit test, but we should have that upstream conversation first.
I don't want to wait until too late to upstream unwinder changes because unwinding is one of the few areas where we are modifying existing code instead of just adding new functionality.

[clayborg]

This logic should go into a function as this code is duplicated below many times. Just create a static function in this file:

static bool CFAIsValid(ABISP abi_sp, lldb::addr_t cfa) {
  if (cfa == LLDB_INVALID_ADDRESS)
    return false;
  if (abi_sp)
    return abi_sp->CallFrameAddressIsValid(cfa)
  else
    return m_cfa != 0 && m_cfa != 1;
}

[pveras]

Addressed comments and created an upstream pull request here: llvm#161398 but will keep this PR around for reference