[llvm] [llvm] Add KnownBits implementations for avgFloor and avgCeil (PR #86445)

[Nhat Nguyen via llvm-commits]

changkhothuychung wrote:

> Any luck with fixing the unit test failures?

no not yet unfortunately, it should be related to the lines in the file SelectionDAG.cpp I highlighted above, be cause the failed test links to those lines, but currently I still struggle figuring out why it fails. 

https://github.com/llvm/llvm-project/pull/86445