[clang] [llvm] [mlir] [polly] [NFC] Rename `Intrinsic::getDeclaration` to `getOrInsertDeclaration` (PR #111752)

[Daniel Chen via cfe-commits]

DanielCChen wrote:

I see. I don't have strong preference although it would be nice to use some function that exists.  

https://github.com/llvm/llvm-project/pull/111752