[clang] Fix diagnostics-dsym.test on mac-arm64 (PR #99399)

[Cyndy Ishida via cfe-commits]

cyndyishida wrote:

Thank you @zeroomega ! I am also running on arm64-mac and that test is passing. What is your `cmake` invocation? I'd like to dig into the underlying cause of non-stable ordering. It looks like the darwin-aarch64 is passing the test as well https://lab.llvm.org/buildbot/#/builders/190 
In general, though, I'm not too worried about the ordering of diagnostics so maybe a `CHECK-DAG` would make the test resilient

https://github.com/llvm/llvm-project/pull/99399