Allow compilation with X.

* src/igc: Turn the error about text conversion into a warning.
  (Figc_roots): Initialize the result.

* src/gtkutil.c (xg_mark_data)
* src/xselect.c (mark_xselect)
* src/xterm.c (mark_xterm): Don't define marking functions when
  compiling with MPS.

src/gtkutil.c

@@ -3025,6 +3025,7 @@ unref_cl_data (xg_menu_cb_data *cl_data)
 
 /* Function that marks all lisp data during GC.  */
 
+#ifndef HAVE_MPS
 void
 xg_mark_data (void)
 {
@@ -3069,6 +3070,7 @@ xg_mark_data (void)
     }
 #endif
 }
+#endif
 
 /* Callback called when a menu item is destroyed.  Used to free data.
    W is the widget that is being destroyed (not used).

src/igc.c

@@ -58,7 +58,8 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>. */
 # error "HAVE_PDUMPER required"
 #endif
 #ifdef HAVE_TEXT_CONVERSION
-# error "HAVE_TEXT_CONVERSION not supported"
+//# error "HAVE_TEXT_CONVERSION not supported"
+# warning "HAVE_TEXT_CONVERSION not supported"
 #endif
 
 /* Note: Emacs will call allocation functions whlle aborting. This leads
@@ -2678,7 +2679,7 @@ DEFUN ("igc-roots", Figc_roots, Sigc_roots, 0, 0, 0, doc : /* */)
 (void)
 {
   struct igc *gc = global_igc;
-  Lisp_Object roots;
+  Lisp_Object roots = Qnil;
 
   for (igc_root_list *r = gc->roots; r; r = r->next)
     {

src/xselect.c

@@ -3488,6 +3488,7 @@ syms_of_xselect_for_pdumper (void)
   property_change_reply = Fcons (Qnil, Qnil);
 }
 
+#ifndef HAVE_MPS
 void
 mark_xselect (void)
 {
@@ -3518,3 +3519,4 @@ mark_xselect (void)
 	mark_object (cs->string);
     }
 }
+#endif

src/xterm.c

@@ -32212,6 +32212,7 @@ init_xterm (void)
 #endif
 }
 
+#ifndef HAVE_MPS
 void
 mark_xterm (void)
 {
@@ -32263,6 +32264,7 @@ mark_xterm (void)
     }
 #endif
 }
+#endif
 
 /* Error handling functions for Lisp functions that expose X protocol
    requests.  They are mostly like `x_catch_errors' and friends, but