[llvm] [LoopInterchange] Ignore the cost-model, force interchange if legal (PR #148858)

[Sjoerd Meijer via llvm-commits]

sjoerdmeijer wrote:

> the behavior when both --loop-interchange-profitabilities=... and --loop-interchange-force=1 are specified. Which one should take precedence in this case? 

I think that should be forcing interchange, which should be the current behaviour. But I am adding `force` as an option to `--loop-interchange-profitabilities=` because I like the idea of having one interface for controlling the cost model. In addition, it solves this problem/unclarity. 

https://github.com/llvm/llvm-project/pull/148858