[pango] One more warning fix

[Matthias Clasen <matthiasc src gnome org>]

commit a7c89dd1eb4c3cf6ebedce193693fceadcdf5995
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Aug 2 07:49:25 2019 -0400

    One more warning fix

 examples/pangowin32tobmp.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)
---
diff --git a/examples/pangowin32tobmp.c b/examples/pangowin32tobmp.c
index 15e473ec..2a945d70 100644
--- a/examples/pangowin32tobmp.c
+++ b/examples/pangowin32tobmp.c
@@ -50,10 +50,13 @@ calc_duration (GTimeVal *tv1, GTimeVal *tv0)
 }
 
 static int
-compare_font_family (PangoFontFamily** a,
-                    PangoFontFamily** b)
+compare_font_family (gconstpointer a,
+                     gconstpointer b)
 {
-  return strcmp (pango_font_family_get_name (*a), pango_font_family_get_name (*b));
+  const PangoFontFamily** aa = (const PangoFontFamily **)a;
+  const PangoFontFamily** bb = (const PangoFontFamily **)b;
+
+  return strcmp (pango_font_family_get_name (*aa), pango_font_family_get_name (*bb));
 }
 
 int main (int argc, char **argv)