Blackbox all whiteboxes after synthesis

This prevents issues like processes in whiteboxes triggering an error in
the JSON backend.

Signed-off-by: gatecat <gatecat@ds0.me>

techlibs/coolrunner2/synth_coolrunner2.cc

@@ -192,6 +192,7 @@ struct SynthCoolrunner2Pass : public ScriptPass
 			run("hierarchy -check");
 			run("stat");
 			run("check -noinit");
+			run("blackbox =A:whitebox");
 		}
 
 		if (check_label("json"))