wcc/ww: reject value-less return in a non-void fn (catB-24)

wwstage's checkretassign short-circuited on a value-less `return;`
("skip flagging for now"), so `fn f() i32 = { return; }` built and
RET'd a garbage register. Mirror cstage cmd/wcc/check.c:2428-2439:
the no-value return has type void, then run isassignable(c.fnret,
void) — void→void and void→(T|void) accept, void→i32 is a confident
reject. cstage already rejected; this aligns wwstage's w6c_ww UP.

Regen w6c/wwdump combined.ww (checker embeds in both). Valid-program
codegen unchanged → cs==ww byte-id gate stays green.

Makefile

@@ -248,6 +248,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_arr_tagged_elem \
 	  $(BIN)/test_dup_main_reject \
 	  $(BIN)/test_tuple_trailing_comma_reject \
+	  $(BIN)/test_voidless_return_reject \
 	  $(BIN)/test_size_untyped_int \
 	  $(BIN)/test_tagged_staticinit \
 	  $(BIN)/test_arr_infer_len \
@@ -1456,6 +1457,12 @@ $(BIN)/test_tuple_trailing_comma_reject: test/wcc/845_tuple_trailing_comma_rejec
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_voidless_return_reject: test/wcc/846_voidless_return_reject.c $(BIN)/ww \
+		$(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
+		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \
+		$(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 $(BIN)/test_tagged_staticinit: test/wcc/843_tagged_staticinit.c $(BIN)/ww \
 		$(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
 		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \