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

[Nikita Popov via llvm-commits]

nikic wrote:

I think the cl::opt option is mainly useful for use with opt rather than clang. (Ideally we'd not use cl::opt for this and instead allow specifying pipeline tuning options from the command line...)

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