MFC r309373 (by bdrewery)

Fix setrlimit_test:setrlimit_memlock when the system has exceeded vm.max_wired.

This uses the same fix as r294894 did for the mlock test. The code from
that commit is moved into a common object file which PROGS supports
building first.

Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D8689