[llvm] [GVN] use `AssertingVH` for leaders to improve compilation time (PR #175870)

[Madhur Amilkanthwar via llvm-commits]

madhur13490 wrote:

This PR lacks a test. Is it possible to add lit test that exercise the path in GVN? Adding a test in Unitetest may test just the moveAssignment and moveConstructors?

https://github.com/llvm/llvm-project/pull/175870