meson: link test-lib{systemd,udev}-sym in the usual way

meson: link test-lib{systemd,udev}-sym in the usual way

I tried to link to the right library by hand, because without
mesonbuid/meson#1545, libbasic.a is added to the link arguments. We want to
link the test with nothing but the library being tested. Doing the linking by
hand did achieve that, but it caused a bigger issue: meson didn't know about
the dependency on the library. And the dependency cannot be added using
link_depends, because "link_depends arguments must be strings...", and this
does not work with a compilation target. So just link in the usual way and
accept the overlinking (for now).