[RFR][openjfx13] JDK-8222788: javafx.web build fails on XCode 10.2

[Arunprasad Rajkumar]

Hi Kevin, Johan,

Please review the following PR. It is just a cherry-pick from upstream WebKit repo to resolve build failure when using Xcode 10.2.

https://github.com/javafxports/openjdk-jfx/pull/474

https://bugs.openjdk.java.net/browse/JDK-8222788

Thanks,
Arun