[clang] [llvm] [HIPSPV] Add in-tree SPIR-V backend support for chipStar (PR #206910)

[Paulius Velesko via cfe-commits]

pvelesko wrote:

Implemented via the existing `-f[no-]integrated-objemitter` flags (same mechanism as the spirv64 toolchain): the in-tree backend is now the default when built, and `-fno-integrated-objemitter` selects the external llvm-spirv. A stray `llvm-spirv` in PATH no longer affects the choice.

https://github.com/llvm/llvm-project/pull/206910