[clang] [clang] Lower modf builtin using `llvm.modf` intrinsic (PR #126750)

[Benjamin Maxwell via cfe-commits]

MacDue wrote:

> So to handle this, we need different lowering in strictfp mode, probably to a "constrained" intrinsic.

I've updated the lowering to simply bail out when `Builder.getIsFPConstrained()` set (which I think corresponds to `strictfp`). So now in the `HAS_MAYTRAP` case the lowering is unchanged. 



https://github.com/llvm/llvm-project/pull/126750