[clang] [llvm] [clang-sycl-linker] Add per-translation-unit device code split mode (PR #196435)

[Maksim Sabianin via cfe-commits]

maksimsab wrote:

nit:
```cpp
return createStringError(inconvertibleErrorCode(), "error message");
```

can be shortened to
```cpp
return createStringError("error message");
```

https://github.com/llvm/llvm-project/pull/196435