SOUND=foo vs !defined(USER_SOUNDS)

Give a better message than "Unknown config statement" if SOUNDDIR or
SOUND directives are found in the configuration file being loaded by
an executable built without support for USER_SOUNDS.  And just give
it for the first occurrence since when present there will likely be
multiple SOUND instances.

It doesn't attempt to deal with the case where the current interface
does not support sound but USER_SOUNDS is enabled because another
interface in the same executable does.

src/decl.c

@@ -407,6 +407,7 @@ const struct instance_globals g_init = {
     NULL, /* config_section_chosen */
     NULL, /* config_section_current */
     0, /* nesting */
+    0, /* no_sound_notified */
     0, /* symset_count */
     FALSE, /* chosen_symset_start */
     FALSE, /* chosen_symset_end */

src/files.c

@@ -2773,7 +2773,15 @@ parse_config_line(char *origbuf)
         sounddir = dupstr(bufp);
     } else if (match_varname(buf, "SOUND", 5)) {
         add_sound_mapping(bufp);
-#endif
+#else /* !USER_SOUNDS */
+    } else if (match_varname(buf, "SOUNDDIR", 8)
+               || match_varname(buf, "SOUND", 5)) {
+        if (!g.no_sound_notified++) {
+            config_error_add("SOUND and SOUNDDIR are not available.");
+        }
+        ; /* skip this and any further SOUND or SOUNDDIR lines
+           * but leave 'retval' set to True */
+#endif /* ?USER_SOUNDS */
     } else if (match_varname(buf, "QT_TILEWIDTH", 12)) {
 #ifdef QT_GRAPHICS
         extern char *qt_tilewidth;