[llvm] [ADT] ImutAVLFactory: avoid overhead of vector for freelist (PR #196534)

[Gábor Horváth via llvm-commits]

Xazax-hun wrote:

Ah sorry, maybe I misunderstood! Actually, there are two sets of pointers. One used for canonicalization for an intrusive linked list, and one for left/right. We still have the left/right pointers, so you should be able to reuse them for the freelist even after my changes. 

https://github.com/llvm/llvm-project/pull/196534