[llvm] [LLVM] Add option to store Parent-pointer in ilist_node_base (PR #94224)

[Stephen Tozer via llvm-commits]

SLTozer wrote:

> @SLTozer There is a compilation failure in LLVM unit tests (IListBaseTest.cpp).

Ah, I missed the unit tests! Fixed the compilation errors and added some tests for the new ilist_node_base behaviour; I'll also add some unit tests for the other IList classes that got functional changes in this patch.

https://github.com/llvm/llvm-project/pull/94224