/usr/share/doc/cpp-7-x86-64-linux-gnux32 is in cpp-7-x86-64-linux-gnux32 7.3.0-16ubuntu3cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/gcc-7-x86-64-linux-gnux32-base
/usr/share/doc/gcc-7-x86-64-linux-gnux32-base