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

[Yingwei Zheng via cfe-commits]

dtcxzyw wrote:

> TBH I am wondering if we should revert this rename. I don't think it's a good idea to reuse getDeclaration with substantially different semantics, and if we're not reusing it, then there's not much point to rename...
> 
> Instead of having getOrInsertDeclaration + getDeclaration with a meaning inversion, we can have getDeclaration and getDeclarationIfExists without the inversion.

I'd like to revert this change, or just add `Intrinsic::getDeclaration` back and mark it as deprecated. I have encountered a build error on Alive2.


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