[llvm] [Demangle] demangle builtin type transformations (PR #65902)

[Shafik Yaghmour via llvm-commits]

shafik wrote:

It looks like in: https://github.com/llvm/llvm-project/issues/62127 I identified that this was brought in via: https://github.com/llvm/llvm-project/commit/e9ef45635b77598fc9ce0cd38d7d3f8c9d88a49d

Do we need to add tests for the other builtins as well, just to verify that we don't have other issues? It is not obvious to me why this effects only `__decay`.

https://github.com/llvm/llvm-project/pull/65902