Avoid redefining kotlin2js task in "ant jslib"

This helps to specify custom runtime for the newly built kotlin2js (which is
supposed to be different for the two bootstrapping steps). Also now it's not
required to launch ant-tools task before jslib to build JS library

build.xml

@@ -217,24 +217,52 @@
         </if>
     </target>
 
-    <target name="compile-kotlin-js-stdlib">
-        <typedef resource="org/jetbrains/jet/buildtools/ant/antlib.xml" classpath="${kotlin-home}/lib/kotlin-ant.jar"/>
+    <macrodef name="new-kotlin2js">
+        <attribute name="output"/>
+        <element name="src"/>
 
+        <sequential>
+            <local name="src.line"/>
+
+            <path id="src.path">
+                <src/>
+            </path>
+
+            <pathconvert property="src.line" refid="src.path" pathsep=" "/>
+
+            <java classname="org.jetbrains.jet.cli.js.K2JSCompiler" failonerror="true" fork="true">
+                <classpath>
+                    <file file="${bootstrap.runtime}"/>
+                    <pathelement location="${kotlin-home}/lib/kotlin-compiler.jar"/>
+                </classpath>
+                <assertions>
+                    <enable/>
+                </assertions>
+                <arg line="${src.line}"/>
+                <arg value="-output"/>
+                <arg value="@{output}"/>
+                <arg value="-no-stdlib"/>
+                <arg line="-main noCall"/>
+            </java>
+        </sequential>
+    </macrodef>
+
+    <target name="compile-kotlin-js-stdlib">
         <property name="compiled.builtins.js" value="builtins.js"/>
         <property name="compiled.stdlib.js" value="stdlib.js"/>
         <property name="stdlib.js.dir" value="${basedir}/js/js.translator/testData"/>
 
-        <kotlin2js output="${output}/${compiled.builtins.js}" noStdlib="true" main="noCall">
+        <new-kotlin2js output="${output}/${compiled.builtins.js}">
             <src>
                 <fileset refid="kotlin.builtin.files"/>
             </src>
-        </kotlin2js>
+        </new-kotlin2js>
 
-        <kotlin2js output="${output}/${compiled.stdlib.js}" noStdlib="true" main="noCall">
+        <new-kotlin2js output="${output}/${compiled.stdlib.js}">
             <src>
                 <resources refid="js.lib.files"/>
             </src>
-        </kotlin2js>
+        </new-kotlin2js>
 
         <taskdef name="closure-compiler"
                  classname="com.google.javascript.jscomp.ant.CompileTask"