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

[Helena Kotas via cfe-commits]

https://github.com/hekota approved this pull request.

LGTM! Please add a note to the PR description about why is are you changing atan2 to erff in clang/test/CodeGenCXX/builtin-calling-conv.cpp.

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