The syscall SYS_sigreturn was unblocked in <https://commits.webkit.org/255036@main>, but it turns out it is sufficient to block it without the default process termination behavior.
<rdar://100604972>
Pull request: https://github.com/WebKit/WebKit/pull/4983
Committed 255462@main (43c46e90c400): <https://commits.webkit.org/255462@main> Reviewed commits have been landed. Closing PR #4983 and removing active labels.