update_gtk_icon_cache: Fix for GTK4-only builds

Try to execute both gtk-update-icon-cache and
gtk4-update-icon-cache after checking whether the
commands are available.

This attempts to match what gtk-icon-cache.bbclass is doing.

This fixes running update_gtk_icon_cache during do_rootfs
for an image that contains only GTK4 related packages.

(From OE-Core rev: 1e01ef59a5864f1261e9c0ca76fcccee2eb7e7f3)

Signed-off-by: Zoltán Böszörményi <zboszor@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/postinst-intercepts/update_gtk_icon_cache

@@ -11,7 +11,11 @@ $STAGING_DIR_NATIVE/${libdir_native}/gdk-pixbuf-2.0/gdk-pixbuf-query-loaders --u
 
 for icondir in $D/usr/share/icons/*/ ; do
     if [ -d $icondir ] ; then
-        gtk-update-icon-cache -fqt  $icondir
+        for gtkuic_cmd in gtk-update-icon-cache gtk4-update-icon-cache ; do
+            if [ -n "$(which $gtkuic_cmd)" ]; then
+                $gtkuic_cmd -fqt  $icondir
+            fi
+        done
     fi
 done