Small JRuby build fixes

[headius]

Two fixes here:

• Add JRuby build output to the CLEAN FileList and Ragel-generated code to the CLOBBER FileList.
• When building on JDK 9+, use --release to specify Java 8 compatibility (fixes Modify JRuby ext build to specify JDK release version #862).

[headius]

@byroot I don't think rake clean and rake clobber are cleaning anything for CRuby either:

[] json $ ls tmp
arm64-darwin24
[] json $ cx 3.4.5 rake clean  
[] json $ ls tmp
arm64-darwin24

[headius]

This is good to go. I did not make any changes to fix rake clean and rake clobber on CRuby.