JDK 9 has deprecated for removal all the EE modules including under this
ID : https://bugs.openjdk.java.net/browse/JDK-8181702, the JAXB APIs.

The building of Nimbus L&F uses this during the build process to
process a file skin.laf
NIMBUS_SKIN_FILE = $(JDK_TOPDIR)/src/java.desktop/share/classes/javax/swing/plaf/nimbus/skin.laf

So we need to remove the dependency in an upcoming release before
the removal happens.

The parsing is done by code below found in the file
jdk/make/src/classes/build/tools/generatenimbus/Generate.java

            JAXBContext ctx = JAXBContext.newInstance("build.tools.generatenimbus");
            Unmarshaller u = ctx.createUnmarshaller();
            SynthModel model = (SynthModel) u.unmarshal(skinFile);


This is invoked from make/gensrc/GenSrcSwing.gmk

There are 3 options I can think of
(1) Import a parser into JDK to parse the skin.laf
(2) Add a new build tool dependency which is an external JAXB implementation
(3) Remove the build dependency by saving the generated source files
and checking them into the repository

That last option seems like the least work and risk.
The build time generation was useful when the skins were being updated
during development but they are never (or almost never) updated any more
and SFAIK is is all cross-platform so building once should suffice.

The Generate tool should remain but used only by a script which relies
on an external JAXB implementation for that rare case the skin needs
to be re-generated.

This might even speed up the build a little ..