[llvm] [MC] Fix quadratic runtime within alignment boundary fragment relaxation (PR #176535)

[Fabian Parzefall via llvm-commits]

pzfl wrote:

> MCBoundaryAlignFragment is a work around, which becomes less relevant over time.
> I am concerned about its potential impact on the primary code path used by the majority of our users.

Thanks for taking a look so quickly. I agree it's not the nicest fix. When you say it becomes less relevant, is there another alternative to achieve this kind of alignment for branch instructions? Or do you have anything in mind in which direction this code should be taken?

https://github.com/llvm/llvm-project/pull/176535