/usr/include/gmerlin/gui_gtk/ is in libgmerlin-dev 1.2.0~dfsg+1-6.1build1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/gmerlin/gui_gtk/aboutwindow.h
/usr/include/gmerlin/gui_gtk/albumentry.h
/usr/include/gmerlin/gui_gtk/audio.h
/usr/include/gmerlin/gui_gtk/auth.h
/usr/include/gmerlin/gui_gtk/button.h
/usr/include/gmerlin/gui_gtk/chapterdialog.h
/usr/include/gmerlin/gui_gtk/display.h
/usr/include/gmerlin/gui_gtk/driveselect.h
/usr/include/gmerlin/gui_gtk/fileentry.h
/usr/include/gmerlin/gui_gtk/fileselect.h
/usr/include/gmerlin/gui_gtk/gtkutils.h
/usr/include/gmerlin/gui_gtk/infowindow.h
/usr/include/gmerlin/gui_gtk/logwindow.h
/usr/include/gmerlin/gui_gtk/message.h
/usr/include/gmerlin/gui_gtk/multiinfo.h
/usr/include/gmerlin/gui_gtk/plugin.h
/usr/include/gmerlin/gui_gtk/presetmenu.h
/usr/include/gmerlin/gui_gtk/question.h
/usr/include/gmerlin/gui_gtk/scrolltext.h
/usr/include/gmerlin/gui_gtk/slider.h
/usr/include/gmerlin/gui_gtk/textview.h
/usr/include/gmerlin/gui_gtk/tree.h
/usr/include/gmerlin/gui_gtk/urllink.h
/usr/include/gmerlin/gui_gtk/urlselect.h