build: Enable to configure GNOME_PANEL_MODULES_DIR
On NixOS, we would like to tell gnome-applets to not install it's modules to gnome-panel's prefix, but to gnome-applets' prefix. This is because our build system doesn't allow one build to change the contents produced by other builds. In version 3.36.4, this was possible with the configure flag --with-libpanel-applet-dir
. But I couldn't track down what change to configure.ac
removed this flag. This patch allows to set the same value via GNOME_PANEL_MODULES_DIR
flag.