FindGTK2: Add harfbuzz to GTK2_INCLUDE_DIRS

Fixes: #19531

Modules/FindGTK2.cmake

diff --git a/Modules/FindGTK2.cmake b/Modules/FindGTK2.cmake
index e3af676..83091f3 100644
--- a/Modules/FindGTK2.cmake
+++ b/Modules/FindGTK2.cmake
@@ -259,6 +259,7 @@
         gtkmm-2.4
         libglade-2.0
         libglademm-2.4
+        harfbuzz
         pango-1.0
         pangomm-1.4
         sigc++-2.0
@@ -711,6 +712,8 @@
         _GTK2_FIND_LIBRARY    (PANGO pango false true)
         _GTK2_ADD_TARGET      (PANGO GTK2_DEPENDS gobject glib)
 
+        _GTK2_FIND_INCLUDE_DIR(HARFBUZZ hb.h)
+
         _GTK2_FIND_LIBRARY    (PANGOCAIRO pangocairo false true)
         _GTK2_ADD_TARGET      (PANGOCAIRO GTK2_DEPENDS pango cairo gobject glib)