[libclc] [libclc] Reduce bithacking in CLC frexp (PR #129871)

[Romaric Jodin via cfe-commits]

rjodinchr wrote:

yes wrong results:
```
ERROR: frexp: {-8404992.000000, 139} ulp error at 0x1.008p-140: *{0x1.008p-1, -139} vs. {0x1.008p-140, 0}
```

https://github.com/llvm/llvm-project/pull/129871