[llvm] `__builtin.canonicalize` in common code (PR #142105)

[Dominik Steenken via llvm-commits]

dominik-steenken wrote:

Ok, so i updated the comment as requested, got rid of the `undef` check in order to remove the error from the `undef` deprecator and added a bunch of `setOperationAction(..., Legal)` to various backends that had independently handled `fcanonicalize` via their Tablegen files in order to get the tests clean again. Would appreciate another review, especially from folks of the backends that i had to touch in order to fix the tests :).

https://github.com/llvm/llvm-project/pull/142105