[llvm] [X86][CodeGen] Add base atan2 intrinsic lowering (p4) (PR #110760)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon commented:

please can you rebase? I've added the missing declarations to the strict libcall tests to make this PR atan2 specific

https://github.com/llvm/llvm-project/pull/110760