Pass lib in RAKULIB instead of -I in harness6
Pass lib in RAKULIB instead of -I in harness6

Otherwise, child processes will not see the libdir, and tests will fail

rakudo/rakudo,tbrowder/rakudo,rakudo/rakudo,rakudo/rakudo,MasterDuke17/rakudo,labster/rakudo,MasterDuke17/rakudo,labster/rakudo,labster/rakudo,salortiz/rakudo,labster/rakudo,salortiz/rakudo,tbrowder/rakudo,rakudo/rakudo,salortiz/rakudo,tbrowder/rakudo,tbrowder/rakudo,rakudo/rakudo,salortiz/rakudo,salortiz/rakudo,MasterDuke17/rakudo,salortiz/rakudo,tbrowder/rakudo,labster/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,labster/rakudo,MasterDuke17/rakudo,rakudo/rakudo,tbrowder/rakudo