LLVM-C: SimpleLoopUnswitchPass

Legacy LoopUnswitchPass was removed in ⚙ D124376 [Passes] Remove legacy LoopUnswitch pass., and it does not look like its modern replacement is part of LLVM-C.

Should this pass be added to C bindings? It looks like simply adding it to the bindings would not be too hard, not sure what else should be taken into consideration. I’d be happy to do the work.

We could add a C binding for it, but those C bindings are for the legacy pass manager which is in the process of being removed (at least for the optimization pipeline, which loop unswitching is part of). Consider using the new pass manager C bindings (llvm/include/llvm-c/Transforms/PassBuilder.h).

Opened a review to add the binding: ⚙ D127323 Provide SimpleLoopUnswitch binding for legacy pass manager