Fix and enable SysV IPC tests.

Don't declare some types that FreeBSD incorrectly declares.

Fix an incorrect call to open() (missing mode).

ANSIfy prototypes.

Enable SysV message queue, semaphore, and shared memory tests.

With exception of the workaround for union semun, these fixes have been
committed to NetBSD.

Reviewed by: asomers
Approved by: CheriBSD
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D13471