[lld][MachO] Disable read-workers.s test eveywhere

The ASAN bot failed on my previous fix for builds without
threading support:
https://lab.llvm.org/buildbot/#/builders/24/builds/13751

However that build does have threading enabled, so I do
not think my change is the cause. I think the cause is
what #157917 will address:
> The new PR moves to use madvise() instead of the ad-hoc page referencing code I wrote which should avoid SIGSEGVs if the buffer is deallocated.

While that is being reviewed, do not run this test
anywhere. Though the failure I saw was with ASAN, I
think it could happen anywhere.

lld/test/MachO/read-workers.s

@@ -1,4 +1,7 @@
 # REQUIRES: x86 && thread_support
+## Sometimes fails, particularly in an ASAN build, do not run until
+## https://github.com/llvm/llvm-project/pull/157917 addresses the cause.
+# UNSUPPORTED: target={{.*}}
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
 
 ## A non-negative integer is allowed.