[clang] [HIP] fix host-used external kernel (PR #83870)

[Artem Belevich via cfe-commits]

https://github.com/Artem-B approved this pull request.

LGTM in principle, but I'd run it by someone with more familiarity with linking quirks.

@MaskRay PTAL, when you get a chance.

https://github.com/llvm/llvm-project/pull/83870