Disable doclint when generating javadoc with Java 8

Given that emul-ezt requires Java 8, it's easier to just run
"ant doc" with Java 8, but then javadoc choked on many lint
issues, so let's disable doclint altogether and eventually fix
the issues later (or not).

Change-Id: I2a285b16e3713adcda6fa5a621fbb463a2aca234
diff --git a/doc/build.xml b/doc/build.xml
index 0ed5039..8bd05b6 100644
--- a/doc/build.xml
+++ b/doc/build.xml
@@ -1,4 +1,4 @@
-<project name="doc" default="all" basedir=".">
+<project name="doc" default="all" basedir="." xmlns:if="ant:if">
   <property name="gwt.root" location=".." />
   <property name="project.tail" value="doc" />
   <import file="${gwt.root}/common.ant.xml" />
@@ -81,6 +81,7 @@
     <property file="${gwt.root}/build/out/packages.properties" />
     <java classpathref="DOC_PATH" classname="com.google.doctool.custom.GWTJavaDoclet" fork="yes" failonerror="true">
       <jvmarg value="-Xmx1024m" />
+      <arg value="-Xdoclint:none" if:true="${isJava8}" />
       <arg value="-noindex" />
       <arg value="-notree" />
       <arg value="-quiet" />