[InstCombine] Remove instructions before+after unreachable at same time
There is no need to first remove the instructions before and then
the ones after in two different worklist iterations. We don't need
to worry about change reporting here, as the functions do that
themselves.
This avoids the issue in #150338, but not really in a principled
way. It's possible that we will have to allow poison arguments
to lifetime.start/lifetime.end again if this turns out to be a
recurring problem.
llvm-project
be6bed4d - [InstCombine] Remove instructions before+after unreachable at same time
