OSX ant file not found

[mgsx-dev]

When building natives with gradle on OSX, xml files can't be found by Ant.

Workaround is to run each scrips manually :

$ ant -f jni/build-macosx32.xml -v -Dhas-compiler=true clean postcompile
$ ant -f jni/build-macosx64.xml -v -Dhas-compiler=true clean postcompile