The NetBSD libc tests use several definitions/macros that aren't available in
FreeBSD

Add the missing compat definitions/macros to lib/libnetbsd so the testcases
can be compiled with libnetbsd without having to invent ad hoc #define's, or
having to convert things over to FreeBSD idioms

Reviewed by: brooks
Phabric: D993
Sponsored by: EMC / Isilon Storage Division