/usr/lib/gcc/x86_64-linux-gnu/7/plugin/libcp1plugin.so is in gcc-7 7.3.0-16ubuntu3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc/x86_64-linux-gnu/7/plugin/libcp1plugin.so.0.0.0
/usr/lib/gcc/x86_64-linux-gnu/7/plugin/libcp1plugin.so.0.0.0