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

[Matt Arsenault via cfe-commits]

https://github.com/arsenm commented:

Is the build using  `-Xclang -fdenormal-fp-math=dynamic` already? If not it should do that globally 

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