/usr/lib/pkgconfig/x86_64-linux-gnu/libgcj.pc is in gcj-jdk 4:4.6.3-1ubuntu5.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/pkgconfig/x86_64-linux-gnu/libgcj12.pc
/usr/lib/pkgconfig/x86_64-linux-gnu/libgcj12.pc