This allows the unwinder to handle code with mid-function epilogues
where the subsequent code is reachable through a backwards branch.
Two changes are required to accomplish this:
1. Do not enqueue the subsequent instruction if the current instruction
is a barrier(*).
2. When processing an instruction, stop ignoring branches with negative
offsets.
(*) As per the definition in LLVM's MC layer, a barrier is any
instruction that "stops control flow from executing the instruction
immediately following it". See `MCInstrDesc::isBarrier` in MCInstrDesc.h
Part of a sequence of PRs:
[lldb][NFCI] Rewrite UnwindAssemblyInstEmulation in terms of a CFG visit
#169630
[lldb][NFC] Rename forward_branch_offset to branch_offset in
UnwindAssemblyInstEmulation #169631
[lldb] Add DisassemblerLLVMC::IsBarrier API #169632
[lldb] Handle backwards branches in UnwindAssemblyInstEmulation #169633
commit-id:fd266c13
4e4763a8a4