[hip] Fix device-only relocatable code compilation.

Summary:
- In HIP, just as the regular device-only compilation, the device-only
  relocatable code compilation should not involve offload bundle.
- In addition, that device-only relocatable code compilation should have
  the similar 3 steps, namely preprocessor, compile, and backend, to the
  regular code generation with `-emit-llvm`.

Reviewers: yaxunl, tra

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D81427