Estimated hours taken: 3
Branches: main
Make sure the Java back-end puts class files in the right place with
`--use-subdirs' and properly cleans up all generated .class files.
mercury/compiler/compile_target_code.m:
mercury/scripts/Mmake.rules:
Tell to Java compiler to put generated .class files in the
`Mercury/classs' directory.
mercury/compiler/modules.m:
Clean up all generated .class files.