avoid unbounded signal delivery time for signal arriving at ibl hit path ind jmp

Xref #2019 (closed) which adds unlinking of the target of an ibl when a signal arrives while in the middle of the ibl. The solution there punted on handling a signal arriving at the actual ind jmp on the hit path: there the target-holding register has been restored. This issue covers checking for this precise instruction and handling it whether via unlinking or adding general translation support to this case.