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

[Nikita Popov via cfe-commits]

nikic 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!

The use of LLVM symbols in this file is incidental -- it's just a data set of mangled C++ symbol names. The file should only change if the mangling implementation changes.

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