Resolve Java 21 FTBFS
This MR addresses https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1052573
Changes:
- include java_default.mk provided by java-common
- export JAVA_COMPAT_LEVEL in the rules.
- update patch to use JAVA_COMPAT_LEVEL variable
Testing:
- build is sid chroot with default Java 21 enabled