Initially allow syscall mach in sandbox v2, since it was allowed in v1. Individual sandboxes will deny mach syscalls.
<rdar://problem/101888960>
Pull request: https://github.com/WebKit/WebKit/pull/6070
Committed 256265@main (81941f622bb4): <https://commits.webkit.org/256265@main> Reviewed commits have been landed. Closing PR #6070 and removing active labels.