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

[Stephen Tozer via llvm-commits]

SLTozer wrote:

Looks like I missed a spot - reverting for now, will wait for a bit to see if any other errors fall out from the various configurations on CI before reapplying.

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