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

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> > @petrhosek Can someone explain why the clang executable in these tests is called `llvm` on the Fuchsia bots?
> 
> We enable the [`LLVM_TOOL_LLVM_DRIVER_BUILD`](https://github.com/llvm/llvm-project/blob/48deb3568eb2452ff385b04b8f71c34121f47387/clang/cmake/caches/Fuchsia-stage2.cmake#L40) option where all tools are linked together into a single binary called `llvm` and the build generates symlinks, so for example `clang` would be a symlink to `llvm` which is equivalent to invoking `llvm clang <args>`. The fact that you're seeing just just `llvm` without a second argument for the tool looks like a latent bug.

Interesting, right now it just takes `argv[0]` so we should probably update that logic. Is the expected result in this case `llvm clang` or just `clang`.

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