I think I resolved most differences. Left is that we don't call `gtk-update-icon-cache` and Scintilla's Compat.h
```diff --- 1 2022-02-19 00:09:57.208958194 +0100 +++ 2 2022-02-19 00:20:39.484275455 +0100 @@ -21,7 +21,6 @@ ./include/geany/pluginutils.h ./include/geany/prefs.h ./include/geany/project.h -./include/geany/scintilla/Compat.h ./include/geany/scintilla/SciLexer.h ./include/geany/scintilla/Scintilla.h ./include/geany/scintilla/Scintilla.iface @@ -41,20 +40,13 @@ ./include/geany/toolbar.h ./include/geany/ui_utils.h ./include/geany/utils.h -./lib/geany/classbuilder.la ./lib/geany/classbuilder.so -./lib/geany/export.la ./lib/geany/export.so -./lib/geany/filebrowser.la ./lib/geany/filebrowser.so -./lib/geany/htmlchars.la ./lib/geany/htmlchars.so -./lib/geany/saveactions.la ./lib/geany/saveactions.so -./lib/geany/splitwindow.la ./lib/geany/splitwindow.so -./lib/libgeany.la -./lib/libgeany.so.0.0.0 +./lib/libgeany.so.0 ./lib/pkgconfig/geany.pc ./share/applications/geany.desktop ./share/doc/geany/AUTHORS @@ -82,6 +74,7 @@ ./share/doc/geany/html/images/pref_dialog_vte.png ./share/doc/geany/html/images/replace_dialog.png ./share/doc/geany/html/index.html +./share/doc/geany/LexillaLicense.txt ./share/doc/geany/manual.txt ./share/doc/geany/NEWS ./share/doc/geany/README @@ -214,6 +207,7 @@ ./share/icons/hicolor/24x24/actions/geany-build.png ./share/icons/hicolor/24x24/actions/geany-close-all.png ./share/icons/hicolor/24x24/actions/geany-save-all.png +./share/icons/hicolor/24x24/apps/geany.png ./share/icons/hicolor/32x32/actions/geany-build.png ./share/icons/hicolor/32x32/actions/geany-close-all.png ./share/icons/hicolor/32x32/actions/geany-save-all.png @@ -222,7 +216,6 @@ ./share/icons/hicolor/48x48/actions/geany-close-all.png ./share/icons/hicolor/48x48/actions/geany-save-all.png ./share/icons/hicolor/48x48/apps/geany.png -./share/icons/hicolor/icon-theme.cache ./share/icons/hicolor/scalable/actions/geany-build.svg ./share/icons/hicolor/scalable/actions/geany-close-all.svg ./share/icons/hicolor/scalable/actions/geany-save-all.svg @@ -231,7 +224,6 @@ ./share/icons/Tango/24x24/actions/geany-save-all.png ./share/icons/Tango/32x32/actions/geany-save-all.png ./share/icons/Tango/48x48/actions/geany-save-all.png -./share/icons/Tango/icon-theme.cache ./share/icons/Tango/scalable/actions/geany-save-all.svg ./share/locale/ar/LC_MESSAGES/geany.mo ./share/locale/ast/LC_MESSAGES/geany.mo