/usr/include/gdk-pixbuf-2.0/gdk-pixbuf/ is in libgdk-pixbuf2.0-dev 2.36.5-2+deb9u2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/gdk-pixbuf-2.0/gdk-pixbuf-xlib/gdk-pixbuf-xlib.h
/usr/include/gdk-pixbuf-2.0/gdk-pixbuf-xlib/gdk-pixbuf-xlibrgb.h
/usr/include/gdk-pixbuf-2.0/gdk-pixbuf/gdk-pixbuf-animation.h
/usr/include/gdk-pixbuf-2.0/gdk-pixbuf/gdk-pixbuf-autocleanups.h
/usr/include/gdk-pixbuf-2.0/gdk-pixbuf/gdk-pixbuf-core.h
/usr/include/gdk-pixbuf-2.0/gdk-pixbuf/gdk-pixbuf-enum-types.h
/usr/include/gdk-pixbuf-2.0/gdk-pixbuf/gdk-pixbuf-features.h
/usr/include/gdk-pixbuf-2.0/gdk-pixbuf/gdk-pixbuf-io.h
/usr/include/gdk-pixbuf-2.0/gdk-pixbuf/gdk-pixbuf-loader.h
/usr/include/gdk-pixbuf-2.0/gdk-pixbuf/gdk-pixbuf-macros.h
/usr/include/gdk-pixbuf-2.0/gdk-pixbuf/gdk-pixbuf-marshal.h
/usr/include/gdk-pixbuf-2.0/gdk-pixbuf/gdk-pixbuf-simple-anim.h
/usr/include/gdk-pixbuf-2.0/gdk-pixbuf/gdk-pixbuf-transform.h
/usr/include/gdk-pixbuf-2.0/gdk-pixbuf/gdk-pixbuf.h
/usr/include/gdk-pixbuf-2.0/gdk-pixbuf/gdk-pixdata.h