[llvm] [IR] Avoid UB in `SymbolTableListTraits` (PR #139096)

[Kazu Hirata via llvm-commits]

kazutakahirata wrote:

@dtcxzyw I am no expert in what you are trying to do here, but I wonder if disabling specific warnings with `#pragma clang diagnostic push/ignored/pop` is worth considering.

https://github.com/llvm/llvm-project/pull/139096