In order to build JavaFX on Windows, it is necessary to set the VS150COMNTOOLS environment variable. Microsoft no longer sets VS<ver>COMNTOOLS by default any more, so this is a hold-over from prior versions. It's also error prone since the build will fail with an unfriendly error message for a developer who installs Visual Studio on their system and just runs "gradle".

The JavaFX build system should attempt to locate the visual studio compiler if VS150COMNTOOLS is not set.