[RFR][openjfx12] JDK-8211307: Add prefix to build tools paths

[Arunprasad Rajkumar]

Hi,

Please review the following Github PR,

https://github.com/javafxports/openjdk-jfx/pull/283

https://bugs.openjdk.java.net/browse/JDK-8211307

Thanks,
Arun