When building with -Wno-deprecated-declarations the warnings listed below remain.
When building with -Wno-incompatible-pointer-types the build is successful. => so it seems the three instance of incompatible types are the culprit here. lxterminal.c: In function ‘terminal_new’: lxterminal.c:1205:24: error: passing argument 2 of ‘gtk_style_context_add_provider’ from incompatible pointer type [-Wincompatible-pointer-types] 1205 | box_style_ctx, box_css_provider, | ^~~~~~~~~~~~~~~~ | | | GtkCssProvider * {aka struct _GtkCssProvider *} In file included from /usr/include/gtk-3.0/gtk/gtkicontheme.h:27, from /usr/include/gtk-3.0/gtk/gtk.h:127, from lxterminal.c:28: /usr/include/gtk-3.0/gtk/gtkstylecontext.h:1034:59: note: expected ‘GtkStyleProvider *’ {aka ‘struct _GtkStyleProvider *’} but argument is of type ‘GtkCssProvider *’ {aka ‘struct _GtkCssProvider *’} 1034 | GtkStyleProvider *provider, | ~~~~~~~~~~~~~~~~~~^~~~~~~~ lxterminal.c:1237:19: error: passing argument 1 of ‘g_regex_unref’ from incompatible pointer type [-Wincompatible-pointer-types] 1237 | g_regex_unref(dingus1); | ^~~~~~~ | | | VteRegex * {aka struct _VteRegex *} In file included from /usr/include/glib-2.0/glib.h:78, from lxterminal.c:27: /usr/include/glib-2.0/glib/gregex.h:457:71: note: expected ‘GRegex *’ {aka ‘struct _GRegex *’} but argument is of type ‘VteRegex *’ {aka ‘struct _VteRegex *’} 457 | void g_regex_unref (GRegex *regex); | ~~~~~~~~~~~~~~~~~~~~~^~~~~ lxterminal.c:1238:19: error: passing argument 1 of ‘g_regex_unref’ from incompatible pointer type [-Wincompatible-pointer-types] 1238 | g_regex_unref(dingus2); | ^~~~~~~ | | | VteRegex * {aka struct _VteRegex *} /usr/include/glib-2.0/glib/gregex.h:457:71: note: expected ‘GRegex *’ {aka ‘struct _GRegex *’} but argument is of type ‘VteRegex *’ {aka ‘struct _VteRegex *’} 457 | void g_regex_unref (GRegex *regex); | ~~~~~~~~~~~~~~~~~~~~~^~~~~