/usr/include/Magick++.h is in graphicsmagick-libmagick-dev-compat 1.3.30+hg15796-1~deb9u2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/include/GraphicsMagick/Magick++.h
/usr/include/GraphicsMagick/Magick++.h