[jakarta.ee-community] targeting JDK 8 *and* JDK 11?

[Bill Shannon <bill.shannon@xxxxxxxxxx>]

What's the state of the art for building a jar file that contains class
files that will work on JDK 8, and a module-info.class that will work
on JDK 11?  The last time I looked at this all I found were kludges
that resulted in compiling everything twice, or very complex Maven
configurations that depended on using multiple versions of the JDK
to compile.  Is there a better way?  Is there an existing project
that would be a good example?