[libclc] [libclc] Refine __clc_fp*_subnormals_supported (PR #157633)

[Matt Arsenault via cfe-commits]

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arsenm wrote:

This shouldn't do all of this bithacking. This is canonicalize, which at worst costs an extra instruction you might not have needed. With the pattern from https://github.com/llvm/llvm-project/pull/172998, you can have this conditional flush that doesn't have the cost of signaling nan quieting and can fold away without DAZ 

https://github.com/llvm/llvm-project/pull/157633