Plug the ATF tests into the build.This is a MFC into stable/10 of:- r257849 Add libatf-c++ to the prebuild libs.- r257853 Build and install the atf tests.- r258233 Move all atf directories to the tests mtree.- r258285 Fix the build of some ATF tests.This change is "make tinderbox" clean on ref10-amd64 with the defaultsettings of WITHOUT_TESTS. It is likely for the WITH_TESTS build tostill be broken because not all relevant changes have been merged yet.
Build and install the atf tests.Reviewed by: freebsd-testingApproved by: rpaulo (mentor)