Add checks for whether gdk-pixbuf exists before using avatar set

configure.ac

@@ -65,6 +65,8 @@ AC_ARG_WITH([themes],
     [AS_HELP_STRING([--with-themes[[=PATH]]], [install themes (default yes)])])
 AC_ARG_ENABLE([icons-and-clipboard],
     [AS_HELP_STRING([--enable-icons-and-clipboard], [enable GTK tray icons and clipboard paste support])])
+AC_ARG_ENABLE([gdk-pixbuf],
+    [AS_HELP_STRING([--enable-gdk-pixbuf], [enable GDK Pixbuf support])])
 
 # Required dependencies
 
@@ -306,6 +308,15 @@ if test "x$enable_otr" != xno; then
    AM_COND_IF([BUILD_OTR], [AC_DEFINE([HAVE_LIBOTR], [1], [Have libotr])])
 fi
 
+dnl feature: pixbuf
+AS_IF([test "x$enable_pixbuf" != xno],
+    [PKG_CHECK_MODULES([gdk_pixbuf], [gdk-pixbuf-2.0 >= 2.4],
+        [AC_DEFINE([HAVE_PIXBUF], [1], [gdk-pixbuf module])],
+        [AS_IF([test "x$enable_pixbuf" = xyes],
+               [AC_MSG_ERROR([gdk-pixbuf-2.0 >= 2.4 is required for GDK Pixbuf support])],
+               [AC_MSG_NOTICE([gdk-pixbuf-2.0 >= 2.4 not found, GDK Pixbuf support not enabled])])])])
+
+
 dnl feature: omemo
 AM_CONDITIONAL([BUILD_OMEMO], [false])
 if test "x$enable_omemo" != xno; then