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

[Wenju He via cfe-commits]

wenju-he wrote:

> I think dropping the soft FMA is beyond the scope of this patch, but it is something I think should be done

restored clc_sw_fma in https://github.com/llvm/llvm-project/pull/157633/changes/b61e32b87d54e5f486b6a7a9cbfd818b455bb3d4

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