Initially allow syscall mach in sandbox v3, since it was allowed in v1. Individual sandboxes will deny mach syscalls.
<rdar://problem/103764832>
Pull request: https://github.com/WebKit/WebKit/pull/8169
Committed 258411@main (8c5dd8c31d25): <https://commits.webkit.org/258411@main> Reviewed commits have been landed. Closing PR #8169 and removing active labels.