Show Java compilation issues in the CLI when using the Java 9+ frontend.

jplag.frontend.java-1.9/src/main/java/jplag/java19/JavacAdapter.java

@@ -48,6 +48,7 @@ public class JavacAdapter {
         int errors = 0;
         for (Diagnostic<?> diagItem : diagListen.getDiagnostics()) {
             if (diagItem.getKind() == javax.tools.Diagnostic.Kind.ERROR) {
+                System.out.println(diagItem); // TODO TS: Implement proper logging.
                 errors++;
             }
         }