Here is the error:

src.client.src.shared.build:

src.client.build-java:
[javac] Compiling 2 source files to /var/www/collide/bin/classes
[javac] warning: Supported source version 'RELEASE_7' from annotation processor 'xapi.dev.processor.AnnotationMirrorProcessor' less than -source '1.8'
[javac] warning: Supported source version 'RELEASE_7' from annotation processor 'xapi.dev.processor.InjectionAnnotationProcessor' less than -source '1.8'
[javac] /var/www/collide/java/com/google/collide/client/testing/DebugAttributeSetter.java:104: error: reference to on is ambiguous
[javac] on(Elements.asJsElement(element));
[javac] ^
[javac] both method on(elemental.dom.Element) in DebugAttributeSetter and method on(com.google.gwt.dom.client.Element) in DebugAttributeSetter match
[javac] 1 error
[javac] 2 warnings

BUILD FAILED
/var/www/collide/java/com/google/collide/client/build.xml:49: The following error occurred while executing this line:
/var/www/collide/macros.ant.xml:126: Compile failed; see the compiler error output for details.

Total time: 1 second

MY MACHINE:

ant -version
Apache Ant(TM) version 1.9.3 compiled on April 8 2014

java -version
java version "1.8.0_20"
Java(TM) SE Runtime Environment (build 1.8.0_20-b26)
Java HotSpot(TM) 64-Bit Server VM (build 25.20-b23, mixed mode)