This reverts commit d7efac1be1441c122f7fb9de51a409172f21326c.
This reverts commit 9d0eea9422d075c8a6924b33161d2d5abfb4072a.
Some ports (specifically Python) define BSD_VISIBLE themselves, so
the change from BSD_VISIBLE to __POSIX_VISIBLE >= 202405 makes them
fail.