https://bugs.openjdk.java.net/browse/JDK-8258465 recognised that a headless build needs X11 headers.

Seems like shared code relies on having platform-specific Rect definitions so when you port to a new platform you need to define a new one.

There might be some good reason for this but it would be nice
to run it to ground. And even if it is reasonable perhaps if
#ifdef HEADLESS
..

we can use some definition that isn't dependent on a platform