[clang] [AMDGPU][SPIR-V] Fix treating SPIR-V input as the wrong LLVM-IR (PR #202986)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

So, easy solution is to just hack in some special detection for `-Xarch` LTO. That would give the control without modifying the status quo. A better but more destructive solution would be to deprecate `-foffload-lto` and alias it to `-Xarch_device -flto` and have `-flto` enable it for both host / device.

https://github.com/llvm/llvm-project/pull/202986