Since !7039 (merged) we do not consider llvm-ar at all on Apple
platforms. However, there are existing cross-compiling use cases in
which the toolchain has llvm-ar but not ar. Prior to the
re-ordering in !6164 (merged), we preferred
ar and then llvm-ar. Restore the original order for Apple.
Fixes: #23320 (closed)
Issue: #23333
Backport: release