[clang] [llvm] Reland "[HIPSPV] Add in-tree SPIR-V backend support for chipStar" (PR #213052)

[Paulius Velesko via cfe-commits]

pvelesko wrote:

@yxsamliu Updated: commit 1 relands #206910 unmodified, commit 2 is the fix, commit 3 adds a test not guarded by spirv-registered-target.

Tested in X86;SPIRV and X86 only builds. Driver tests pass in both. Non-RDC and RDC (new driver, cross-TU) flows were run for real: the X86 only build emits through llvm-spirv, the X86;SPIRV build through the in-tree backend, both spirv-val clean.

RDC with the old offload driver fails in both configurations, but reproduces with the pre-#206910 sources on the same LLVM, so it is pre-existing on main.

https://github.com/llvm/llvm-project/pull/213052