https://bugs.gentoo.org/708520
https://github.com/carlobaldassi/gimp-lqr-plugin/issues/7
--- a/src/interface_aux.c	2013-08-05 06:06:03.000000000 -0700
+++ b/src/interface_aux.c	2020-10-06 10:44:45.349564022 -0700
@@ -48,11 +48,11 @@
 
 gint dialog_aux_response = GTK_RESPONSE_OK;
 
-PlugInUIVals *ui_state;
-PlugInVals *state;
-PlugInDialogVals *dialog_state;
+extern PlugInUIVals *ui_state;
+extern PlugInVals *state;
+extern PlugInDialogVals *dialog_state;
 
-GtkWidget *dlg;
+extern GtkWidget *dlg;
 
 /***  Public functions  ***/
 
--- a/src/interface_I.c	2013-08-05 06:06:03.000000000 -0700
+++ b/src/interface_I.c	2020-10-06 10:44:45.349564022 -0700
@@ -65,13 +65,13 @@
 
 gint dialog_I_response = GTK_RESPONSE_OK;
 
-PlugInUIVals *ui_state;
-PlugInVals *state;
-PlugInDialogVals *dialog_state;
-gboolean features_are_sensitive;
+extern PlugInUIVals *ui_state;
+extern PlugInVals *state;
+extern PlugInDialogVals *dialog_state;
+extern gboolean features_are_sensitive;
 InterfaceIData interface_I_data;
 
-GtkWidget *dlg;
+extern GtkWidget *dlg;
 GtkWidget *coordinates;
 
 gulong size_changed = 0;
--- a/src/main.c	2013-08-05 06:06:03.000000000 -0700
+++ a/src/main.c	2020-10-06 10:44:45.349564022 -0700
@@ -179,7 +179,7 @@
   {GIMP_PDB_INT32, "resize_aux_layers",
    "Whether to resize auxiliary layers"},
   {GIMP_PDB_INT32, "resize_canvas", "Whether to resize canvas"},
-  {GIMP_PDB_INT32, "output target", "Output target (same layer, new layer, new image)"},
+  {GIMP_PDB_INT32, "output_target", "Output target (same layer, new layer, new image)"},
   {GIMP_PDB_INT32, "seams", "Whether to output the seam map"},
   {GIMP_PDB_INT32, "nrg_func", "Energy function to use"},
   {GIMP_PDB_INT32, "res_order", "Resize order"},