[clang] [llvm] [mlir] [polly] [IR][NFC] Update IRBuilder to use InsertPosition (PR #96497)

[Nikita Popov via cfe-commits]

nikic wrote:

Looks like using InsertPosition in IRBuilder has some overhead: https://llvm-compile-time-tracker.com/compare.php?from=317277e4f961edf13132914a58a26408db4ab0aa&to=6481dc57612671ebe77fe9c34214fba94e1b3b27&stat=instructions:u

So it might make sense to keep some explicit overloads for IRBuilder (not sure which ones are hot though).

https://github.com/llvm/llvm-project/pull/96497