jdk8u-dev MacOS 10.15+ build environment?

[Andrew Leonard]

Hi,
I have a Mac OS contribution i've developed and tested at AdoptOpenJDK, I
would like to contribute it upstream to jdk8u-dev, unfortunately the
jdk8u-dev supported build platform is MacOS 10.7. Is there a method people
use to build & test their contributions if you don't have a MacOS 10.7
environment? The AdoptOpenJDK jdk8u base has patches to allow building
jdk8u with Xcode 11.5 on 10.15+..
How do others approach Mac contributions?
Thanks
Andrew