[clang] [CIR] Add math and builtin intrinsics support (PR #175233)

[via cfe-commits]

adams381 wrote:

Addressed @andykaylor's feedback on using constrained FP builtins.

**Changes in commit f005f8161f52:**
- Changed `atan2` to use `emitBinaryMaybeConstrainedFPBuiltin` instead of `emitBinaryFPBuiltin`
- Changed `fmod` to use `emitBinaryMaybeConstrainedFPBuiltin` instead of `emitBinaryFPBuiltin`
- Changed all elementwise FP handlers to use `emitUnaryMaybeConstrainedFPBuiltin` (for functions that could raise FP exceptions)
- Grouped `BIforward_like` with the other C++ std:: builtins (`move`, `forward`, `as_const`)

Regarding the suggestion to move elementwise handlers to be grouped with their corresponding functions in `tryEmitFPMathIntrinsic()` - this would be a larger refactoring that could be done in a follow-up PR if preferred.

https://github.com/llvm/llvm-project/pull/175233