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

[Daniel Chen via llvm-commits]

DanielCChen wrote:

> `test_demangle` should definitely **not** be updated when renaming functions.

Could you please explain a bit more since this is new to me? Thanks in advance!

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