/usr/lib/pkgconfig/ImageMagick++.pc is in graphicsmagick-libmagick-dev-compat 1.3.28-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/pkgconfig/GraphicsMagick++.pc
/usr/lib/pkgconfig/GraphicsMagick++.pc