[llvm] [LoopInterchange] Enable it by default (PR #124911)

[Ryotaro Kasuga via llvm-commits]

kasuga-fj wrote:

> The two remaining blockers for this work are:
> 
>     * [[DA] do not handle GEPs with different types #144088](https://github.com/llvm/llvm-project/pull/144088)
> 
>     * [[Delinearization] Add function for fixed size array without relying on GEP #145050](https://github.com/llvm/llvm-project/pull/145050)
> 
> 
> The former is essentially a type-punning issue that is confusing DA. The latter is about removing getSourceElementType from Delinearization.
> 
> @sebpop abandoned #144088, wasn't happy with that bandaid, and is going to work on a longer term solution. I am still interested in a short term solution though, so am going to see if we can detect this type punning pattern and try to bail.

I'd like to resolve #145503 as well. It's okay if we end up concluding that the current placement is ideal, but I think the pass position should be discussed before enabling it by default.

https://github.com/llvm/llvm-project/pull/124911