sigsuspend(2) on FreeBSD
The text e860b0dd5e5c, as FreeBSD 2.2.9-RELEASE, FreeBSD 2.2.8-RELEASE, FreeBSD 2.2.7-RELEASE, FreeBSD 2.2.6-RELEASE, FreeBSD 2.2.5-RELEASE, FreeBSD 2.2.2-RELEASE shipped it.
atomically release blocked signals and wait for interrupt