[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?

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