The serial build (i.e. JOBS=1) is currently not working because of missing dependencies for jmod. At the time when jmod is called during the build, various files like jvm.cfg and tzdb.dat which are required for the proper working of jmod, are not in place.

The fix is easy, just add the corresponding dependencies to JMOD_TARGETS.

I'd strongly suggest to add a serial build to at least one of your test builds to keep the build sane. Otherwise the dependencies can easily be broken without somebody noticing it because apparently nowadays nobody is ever building with JOBS=1.