[llvm] [ConstantTime][LLVM] Add llvm.ct.select intrinsic with generic SelectionDAG lowering (PR #166702)

[Julius Alexandre via llvm-commits]

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wizardengineer wrote:

The builder just emits the plain CT_SELECT node now. The fallback lowering moved into the legalizer, and 64613ed31ef6 cleans up that path.

https://github.com/llvm/llvm-project/pull/166702