/usr/include/gtksourceviewmm-3.0/ is in libgtksourceviewmm-3.0-dev 3.18.0-3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/buffer.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/completion.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/completionactivation.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/completioncontext.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/completioninfo.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/completionitem.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/completionproposal.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/completionprovider.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/completionwords.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/gutter.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/gutterrenderer.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/gutterrendererpixbuf.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/gutterrenderertext.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/init.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/language.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/languagemanager.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/mark.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/markattributes.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/markup.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/printcompositor.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/buffer_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/completion_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/completionactivation_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/completioncontext_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/completioninfo_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/completionitem_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/completionproposal_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/completionprovider_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/completionwords_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/gutter_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/gutterrenderer_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/gutterrendererpixbuf_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/gutterrenderertext_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/language_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/languagemanager_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/mark_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/markattributes_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/printcompositor_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/style_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/stylescheme_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/styleschememanager_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/undomanager_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/view_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/style.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/stylescheme.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/styleschememanager.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/undomanager.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/view.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/wrap_init.h