Fix some DISPLAY variable related bugs on PGTK

* src/callproc.c (getenv_internal, make_environment_block):
Don't set DISPLAY on non-X GDK backends.  (bug#54844)

src/callproc.c

@@ -85,6 +85,10 @@ extern char **environ;
 #include "nsterm.h"
 #endif
 
+#ifdef HAVE_PGTK
+#include "pgtkterm.h"
+#endif
+
 /* Pattern used by call-process-region to make temp files.  */
 static Lisp_Object Vtemp_file_name_pattern;
 
@@ -1687,6 +1691,7 @@ getenv_internal (const char *var, ptrdiff_t varlen, char **value,
   /* For DISPLAY try to get the values from the frame or the initial env.  */
   if (strcmp (var, "DISPLAY") == 0)
     {
+#ifndef HAVE_PGTK
       Lisp_Object display
 	= Fframe_parameter (NILP (frame) ? selected_frame : frame, Qdisplay);
       if (STRINGP (display))
@@ -1695,6 +1700,7 @@ getenv_internal (const char *var, ptrdiff_t varlen, char **value,
 	  *valuelen = SBYTES (display);
 	  return 1;
 	}
+#endif
       /* If still not found, Look for DISPLAY in Vinitial_environment.  */
       if (getenv_internal_1 (var, varlen, value, valuelen,
 			     Vinitial_environment))
@@ -1812,6 +1818,18 @@ make_environment_block (Lisp_Object current_dir)
     if (NILP (display))
       {
 	Lisp_Object tmp = Fframe_parameter (selected_frame, Qdisplay);
+
+#ifdef HAVE_PGTK
+	/* The only time GDK actually returns correct information is
+	   when it's running under X Windows.  DISPLAY shouldn't be
+	   set to a Wayland display either, since that's an X specific
+	   variable.  */
+	if (FRAME_WINDOW_P (SELECTED_FRAME ())
+	    && strcmp (G_OBJECT_TYPE_NAME (FRAME_X_DISPLAY (SELECTED_FRAME ())),
+		       "GdkX11Display"))
+	  tmp = Qnil;
+#endif
+
 	if (!STRINGP (tmp) && CONSP (Vinitial_environment))
 	  /* If still not found, Look for DISPLAY in Vinitial_environment.  */
 	  tmp = Fgetenv_internal (build_string ("DISPLAY"),