Building a UI toolkit for many different platforms is a complex and challenging endeavor. It requires platform specific tools such as C compilers as well as portable tools like Gradle and the JDK. Which tools must be installed differs from platform to platform. While the OpenJFX build system was designed to remove as many build hurdles as possible, it is necessary to build native code and have the requisite compilers and toolchains installed. On Mac and Linux this is fairly easy, but setting up Windows is more difficult.
If you are looking for instructions to build FX for JDK 8uNNN, they have been archived here.
Do you really want to build OpenJFX? We would like you to, but the latest stable build is already available on the JavaFX website, and JavaFX 8 is bundled by default in in Oracle JDK desktop editions of JDK 8, JDK 9, and the JDK 10 builds8 (9 and 10 also included JavaFX, but were superseded by 11, which does not). There are also some great community builds that may work for you.
Starting with Java 9, and the introduction of the module system, The FX the JavaFX modules are now an integral part of the runtime environment for the desktop. Because of this tie, there is currently no provision or capability for the output of the OpenJFX 9 or later build to be used as an overlay. It is still possible however to develop and enhance OpenJFX, and use that result to build an OpenJDK. (Recheck) We are exploring making this easier, by enabling a developer to build a set of javafx.* modules that can be used with a clean OpenJDK build (without the javafx.* modules). Stay tuned. (Seems complete)
yum install mercurial bison flex gperf ksh pkgconfig \
libpng12-devel libjpeg-devel libxml2-devel \
libxslt-devel systemd-devel glib2-devel gtk2-devel \
libXtst-devel pango-devel freetype-devel
OpenJFX, as with OpenJDK, uses Mercurial as the source control system. You must install some support for using Mercurial. Many (if not all) IDEs include built in support, although the tooling is generally not as good as you might get from a standalone tool.