Work around the lack of definition of union semun per POSIX.

[brooks]

Summary

When feasible do this by adding -D_WANT_SEMUN to CFLAGS or CXXFLAGS.
Where this fails due to ports not honoring C*FLAGS, patch using
__FreeBSD_version to enable the definition.

NOTE: the patches currently use the un-updated __FreeBSD_version value. This will be corrected at commit time.

[brooks]

See also https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=224443

[brooks]

• One more -D_WANT_SEMUN after new exprun.

[brooks]

• Work around the need for union semun, lack of mymsg, and struct name changes

[brooks]

• Rebase
• Remove no longer needed patches (fixed upstream and port updated).

[brooks]

• Update __FreeBSD_version to anticipated value.