Remove Android BuildUtils dependency from jdiff Gradle build

This allows jdiff to be included in standalone gradle builds,
including the Support Library.

Change-Id: I330eda7aa11caa754c71b5a3234e0f0681974cab
diff --git a/build.gradle b/build.gradle
index 74b8b60..a3b15c4 100644
--- a/build.gradle
+++ b/build.gradle
@@ -14,10 +14,10 @@
  * limitations under the License.
  */
 
-import com.android.internal.BuildUtils
-
 apply plugin: 'java'
 
+import javax.tools.ToolProvider
+
 sourceSets {
     main {
         java.srcDirs = ['src']
@@ -25,5 +25,6 @@
 }
 
 dependencies {
-    compile files(BuildUtils.findToolsJar(project))
+    // tools.jar required for com.sun.javadoc
+    compile files(((URLClassLoader) ToolProvider.getSystemToolClassLoader()).getURLs())
 }