.tar.gz releases don't include java-models-library and documentation doesn't explain how to get it

[martinlester]

CBMC version: 5.83.0
Operating system: Debian 12
Exact command line resulting in the issue: cmake --build build
What behaviour did you expect: Successful compilation.
What happened instead: Compilation error about missing java-models-library.

The GitHub .tar.gz source code releases of CBMC don't include java-models-library, which I assume is used by JBMC. So trying to compile results in an error near the end. You can easily git clone the library into the right place manually, but COMPILING.md doesn't mention that. Or you can disable compiling JBMC.

COMPILING.md does mention needing to update git submodules, which gets you java-models-library if you're working from the CBMC git repository, but not from the .tar.gz.

[tautschnig]

I believe we should update the documentation, and not change the packaging: the licensing terms of java-models-library are different.