Environment Information

Provide at least:

• JRuby version (jruby -v) and command line (flags, JRUBY_OPTS, etc)
  jruby 9.4.3.0 (3.1.4) 2023-06-07 3086960792 OpenJDK 64-Bit Server VM 17.0.8+7 on 17.0.8+7 +jit [x86_64-linux]
• Operating system and platform (e.g. uname -a)

Expected Behavior

It should work like on CRuby and TruffleRuby e.g. by returning so on Linux and dylib on Darwin and dll on Windows.

SOEXT is relevant e.g. for FFI.

Actual Behavior

It's nil:

$ jruby -e 'p RbConfig::CONFIG["SOEXT"]'
nil

What is very surprising to me is https://github.com/ruby/prism/blob/bb35e38000cfec301061e1f6742e257eff238c64/lib/prism/ffi.rb#L17 seems to work on JRuby in CI, but does not for me locally.
Maybe FFI/dlopen() accepts to load "/path/to/librubyparser." and appends the right extension?