[clang] Emit constrained atan2 intrinsic for clang builtin (PR #113636)

[Tex Riddell via cfe-commits]

tex3d wrote:

@farzonl 
> Here are just a handful of tests that we might want to update, but there are others:

I'm updating these tests that were called out.  What others do I need to look for?  How do I know if I've found all the tests I need to update?

https://github.com/llvm/llvm-project/pull/113636