/usr/share/java/libgcj-6.3.0.jar is in gcj-6-jre-lib 6.3.0-18+deb9u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/java/libgcj-6.jar
/usr/share/java/libgcj-6.jar