Upstream pango removed these functions from its installed headers in
this commit:

commit d21ea13a22b1cab8c9cb604aa3fcd2ca8073befd
Author: Matthias Clasen <mclasen@redhat.com>
Date:   Thu Jul 4 20:36:00 2019 +0000

    Header cleanup
    
    Abolish the PANGO_ENABLE_BACKEND and PANGO_ENABLE_ENGINE
    defines. All backend-only apis are moved into private
    headers, all apis that were engine-only are marked as
    deprecated, since engines are.

diff --git a/pango.override b/pango.override
index afe43aba3a6ebe81..3e33e1b598322096 100644
--- a/pango.override
+++ b/pango.override
@@ -27,6 +27,12 @@ headers
 #include <pygobject.h>
 #include <pango/pango.h>
 
+/* These internal functions are still exported, so just declare them
+   here.  There does not seem to be a simple way to ween pygtk2 off
+   them.  */
+PangoFontMetrics *pango_font_metrics_new (void);
+const char *pango_font_map_get_shape_engine_type (PangoFontMap *);
+
 typedef struct {
     PyObject *func, *data;
 } PyGtkCustomNotify;