Make single-file classes tolerant to having many main()'s

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

@@ -0,0 +1,23 @@
+<project name="Ant Task Test" default="build">
+    <taskdef resource="org/jetbrains/kotlin/ant/antlib.xml" classpath="${kotlin.lib}/kotlin-ant.jar"/>
+
+    <target name="build">
+        <kotlinc output="${temp}/hello.jar">
+            <src path="${test.data}"/>
+        </kotlinc>
+
+        <java classname="pkg.AKt" fork="true">
+            <classpath>
+                <pathelement location="${temp}/hello.jar"/>
+                <pathelement location="${kotlin.runtime.jar}"/>
+            </classpath>
+        </java>
+
+        <java classname="pkg.BKt" fork="true">
+            <classpath>
+                <pathelement location="${temp}/hello.jar"/>
+                <pathelement location="${kotlin.runtime.jar}"/>
+            </classpath>
+        </java>
+    </target>
+</project>