Minimal change - there are lots more like this.

--- transfig.3.2.5e/fig2dev/dev/genibmgl.c	2006-08-03 17:26:20.000000000 +0100
+++ transfig.3.2.5e/fig2dev/dev/genibmgl.c	2025-07-04 18:38:55.868003031 +0100
@@ -567,7 +567,7 @@
  * set_width - issue line width commands as appropriate
  *		NOTE: HPGL/2 command used
  */
-static set_width(w)
+static void set_width(w)
     int	w;
 {
     static int current_width=-1;