[clang] [llvm] [polly] [LLVM] Add InsertPosition union-type to remove overloads of Instruction-creation (PR #94226)

[Stephen Tozer via cfe-commits]

SLTozer wrote:

Alright, builds now working for LLVM, Clang, Flang, Polly, and MLIR; looks good to merge?

https://github.com/llvm/llvm-project/pull/94226