[clang] [HIP] Replace use of `llvm-mc` with `clang` (PR #112041)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> It should be `llvm clang`. I'm looking into this right now because this change broke all our builders. I think that `clang/lib/Driver/ToolChains/HIPUtility.cpp` doesn't correctly support `LLVM_TOOL_LLVM_DRIVER_BUILD`.

The variable used here is initialized via `argv[0]` in `tools/driver.cpp`. Presumably we need to take `argv[1]` as well if we have this driver build thing.

https://github.com/llvm/llvm-project/pull/112041