IOS: build failure due to incorrect classpath for javah

The IOS build is failing due to a bad classpath for javah in the :extensions project. Here is the failure:

:extensions:compileJava
:extensions:processResources UP-TO-DATE
:extensions:classes
:extensions:jar
:extensions:javahIosExtensions
Error: Class javafx.util.Duration could not be found.
 FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':extensions:javahIosExtensions'.

Process 'command '/localtools/macosx-universal/jdk/jdk1.8.0-b118/bin/javah'' finished with non-zero exit value 1