[llvm] Add atan2 to WebAssembly RuntimeLibcallSignatureTable (PR #112613)

[Farzon Lotfi via llvm-commits]

farzonl wrote:

Could you change the title prefix to `[WebAssembly]`. I've been ask to do that in Past PRs to this backend. 

Maybe the title should be `[WebAssembly] Add atan2 to RuntimeLibcallSignatureTable`

https://github.com/llvm/llvm-project/pull/112613