build.xml: simplify new-kotlinc macro

- passing sources to "-classpath" is no longer needed because the logic was
  implemented in K2JVMCompiler
- skipping javac2 for stdlib is no longer needed because the corresponding
  error is no longer reproducible since "skip" was added to javac2
- get rid of unneeded properties in favor of Ant's toString feature

build.xml

@@ -664,20 +664,12 @@
 
     <macrodef name="new-kotlinc">
         <attribute name="output"/>
-        <attribute name="withJava" default="true"/>
         <element name="src"/>
-        <!-- This element should have been named "classpath" but it conflicts with classpath elements present in java and javac tasks -->
         <element name="class-path"/>
 
         <sequential>
             <cleandir dir="@{output}"/>
 
-            <!-- All properties declared in this macro should be local because otherwise their value won't change after the first run,
-                 which effectively would make this macro non-reusable -->
-            <local name="src.paths"/>
-            <local name="src.line"/>
-            <local name="classpath.paths"/>
-
             <dirset dir="${basedir}" id="src.dirset">
                 <src/>
             </dirset>
@@ -686,12 +678,9 @@
                 <class-path/>
             </path>
 
-            <!-- Source paths separated by the system path separator -->
-            <pathconvert property="src.paths" refid="src.dirset"/>
             <!-- Source paths separated by space (to pass to "arg line" below) -->
+            <local name="src.line"/>
             <pathconvert property="src.line" refid="src.dirset" pathsep=" "/>
-            <!-- Classpath separated by the system path separator -->
-            <pathconvert property="classpath.paths" refid="classpath.path"/>
 
             <java classname="org.jetbrains.kotlin.cli.jvm.K2JVMCompiler" failonerror="true" fork="true">
                 <classpath>
@@ -706,24 +695,18 @@
                 <arg value="@{output}"/>
                 <arg value="-no-stdlib"/>
                 <arg value="-classpath"/>
-                <!-- Include source paths to classpath for Kotlin compiler to resolve symbols from Java sources -->
+                <arg value="${toString:classpath.path}"/>
-                <arg value="${src.paths}${path.separator}${classpath.paths}"/>
             </java>
 
-            <if>
+            <javac2 srcdir="${toString:src.dirset}" destdir="@{output}" debug="true" debuglevel="lines,vars,source"
-                <equals arg1="@{withJava}" arg2="true"/>
+                    includeAntRuntime="false" source="${java.target}" target="${java.target}">
-                <then>
+                <skip pattern="kotlin/jvm/internal/.*"/>
-                    <javac2 srcdir="${src.paths}" destdir="@{output}" debug="true" debuglevel="lines,vars,source" includeAntRuntime="false"
+                <classpath>
-                            source="${java.target}" target="${java.target}">
+                    <path refid="classpath.path"/>
-                        <skip pattern="kotlin/jvm/internal/.*"/>
+                    <!-- Include @{output} here for Java compiler to resolve symbols from Kotlin sources -->
-                        <classpath>
+                    <pathelement location="@{output}"/>
-                            <path refid="classpath.path"/>
+                </classpath>
-                            <!-- Include @{output} here for Java compiler to resolve symbols from Kotlin sources -->
+            </javac2>
-                            <pathelement location="@{output}"/>
-                        </classpath>
-                    </javac2>
-                </then>
-            </if>
         </sequential>
     </macrodef>
 
@@ -734,12 +717,15 @@
                 <include name="core/runtime.jvm/src"/>
                 <include name="core/reflection/src"/>
             </src>
-            <class-path/>
+            <class-path>
+                <!-- Need something to pass to compiler's "-classpath" here -->
+                <pathelement location="core/builtins/src"/>
+            </class-path>
         </new-kotlinc>
     </target>
 
     <target name="stdlib">
-        <new-kotlinc output="${output}/classes/stdlib" withJava="false">
+        <new-kotlinc output="${output}/classes/stdlib">
             <src>
                 <include name="libraries/stdlib/src"/>
             </src>