[llvm] [NFC][LLVM][AsmWriter] Print a comment for unknown intrinsics (PR #146726)

[Rahul Joshi via llvm-commits]

jurahul wrote:

This can help debug issues such as
https://github.com/StanfordLegion/legion/issues/1865#issuecomment-2863656342 (by running llvm-dis on libdevice.10.bc and verifying that there are no Unknown intrinsic comments).

Since using libdevice that ships with CUDA Toolkit with the LLVM upstream NVPTX backend is a common use case for projects like XLA/Triton/Legion, this feature can be helpful to detect any mismatch between the intrinsics supported by upstream LLVM vs what is present in libdevice shipped with CUDA Toollkit. 

https://github.com/llvm/llvm-project/pull/146726