[clang] [HIP] Allow partial linking for `-fgpu-rdc` (PR #81700)

[Yaxun Liu via cfe-commits]

yxsamliu wrote:

> This makes sense overall, though it's very complicated. Generally we just need to make sure these things are private to one group of files. There's a lot more to parse here compared to the `linker-wrapper`.
> 
> Do any of these tests check when called with `-r`? I'm assuming that's the difference here when we decide whether or not to ghoup files by cuid.

Added a test for `-r`

https://github.com/llvm/llvm-project/pull/81700