OpenBSD: Fix system feature definitions
Since !4477 (merged), some sources explicitly enable needed system APIs on some platforms using definitions like _POSIX_C_SOURCE
and _XOPEN_SOURCE
. Drop the definitions for OpenBSD, which provides the POSIX APIs by default.
Update the definitions for OpenBSD using patches from the official OpenBSD package (called ports).
Backport: release
Topic-rename: openbsd-defines
Edited by Brad King