Don't always run code in Ant task tests

But when running code, do it via <java> task, not via custom testing code. Most
of the time the compiled code need not be runned, because it's irrelevant to
the Ant task itself

compiler/testData/integration/ant/jvm/jvmClasspath/build.xml

@@ -3,5 +3,12 @@
 
     <target name="build">
         <kotlinc src="${test.data}/hello.kt" output="${temp}/hello.jar"/>
+
+        <java classname="hello.HelloPackage" fork="true">
+            <classpath>
+                <pathelement location="${temp}/hello.jar"/>
+                <pathelement location="${kotlin.runtime.jar}"/>
+            </classpath>
+        </java>
     </target>
 </project>