[libclc] [libclc] Support fp32 subnormal inputs and outputs in SPIR-V sw fma (PR #233791)

[Wenju He via cfe-commits]

https://github.com/wenju-he approved this pull request.

LGTM. I reproduce the issue on intel gpu:
```
ldexp...
  1:           ldexp fp32
ERROR: ldexp: 0.500000 ulp error at {-0x1.fffffcp-127 (0x807fffff), -1}: *-0x1p-127 (0x80400000) vs. -0x1.fffff8p-128 (0x803fffff) at index: 1116
  2:           ldexp fp64
ERROR: ldexp: inf ulp error at {-nan, 1}: *-nan vs. -inf
ldexp FAILED
```
fp32 passes after this PR.
The fp64 fail is an existing issue that is not related to this PR. So I can't verify the fp64 fix.

https://github.com/llvm/llvm-project/pull/233791