Revert "Revert "[compiler-rt][Darwin] Add arm64 to simulator platforms""

This reverts commit 3469cb14.

Relanding the patch on behalf of Byoungchan Lee.

The original patch (8a3afc6d) was
reverted because it appeared to be landed without the approval
of an Apple engineer.

After internal discussion we're happy for this to land and I've
formally approved the patch in phabricator
(https://reviews.llvm.org/D119174).

rdar://92134140