[clang] [llvm] [ImmutableSet] Optimize add/remove operations to avoid redundant tree modifications (PR #159845)

[Utkarsh Saxena via llvm-commits]

usx95 wrote:

> Did we only have this issue with the sets? Are the maps fine?

Maps are implemented as a set of key, value pair and therefore use the same API.

https://github.com/llvm/llvm-project/pull/159845