[llvm] [Dexter] Extend XFAIL of Dexter tests to all MacOS architectures. (PR #83936)

[via llvm-commits]

dyung wrote:

> @adrian-prantl I noticed that you removed the XFAIL for all of darwin in [536e0eb](https://github.com/llvm/llvm-project/commit/536e0ebaaa842471ae91bbda4f8cc1821690861e), and then the test started to fail on one of my bots https://lab.llvm.org/buildbot/#/builders/280/builds/68, and I am guessing it will be failing on my other bot (https://lab.llvm.org/staging/#/builders/188) once it gets to your commit.
> 
> Are the bots I setup misconfigured in some manner? These tests have always been failing for me on the x86 bot at least (see https://lab.llvm.org/staging/#/builders/188/builds/400 for example), and it never failed previously on the AArch64 bot because it was previously XFAIL'd there as well.

As expected, the two tests are failing now on my x86 bot as well: https://lab.llvm.org/staging/#/builders/188/builds/575

https://github.com/llvm/llvm-project/pull/83936