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

[Stephen Tozer via llvm-commits]

SLTozer wrote:

Latest update, there's no major impact on compile times [(results)](http://llvm-compile-time-tracker.com/compare.php?from=9e63632b3274dc1b20502b569e79a311977e0a97&to=8095aff5f9a842994a36d085158c9d1e476cd5a9&stat=instructions:u); the only cost is the time to build clang, which as noted will be fixed by the next patch along.

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