wcc: nodeisunsigned N_CALL reads stamped type_ (#168)

Twin of #134 (N_INDEX arm): the wwstage signedness classifier did not
consult the checker-stamped type_ for an N_CALL result, so an
unsigned-returning call got signed IDIVQ/SARQ instead of DIVQ/SHRQ.
cstage was already correct (reads the stamped operand type; check.c:1433),
so this is a wwstage-only arm — symmetric outcome both stages.

Gate-blind (the bootstrap lacks the shape) — covered by table-driven
runtime probe 906, which also asserts w6c==w6c_ww .s byte-identity.

Makefile

@@ -334,6 +334,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_idx_compound_run \
 	  $(BIN)/test_dotbase_arr_run \
 	  $(BIN)/test_continue_run \
+	  $(BIN)/test_callret_unsigned_arith_run \
 	  $(BIN)/test_sar_shr_run \
 	  $(BIN)/test_def_mangle_run \
 	  $(BIN)/test_arr_u16_store_run \
@@ -1141,6 +1142,12 @@ $(BIN)/test_sar_shr_run: test/wcc/912_sar_shr_run.c $(BIN)/ww \
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_callret_unsigned_arith_run: \
+		test/wcc/906_callret_unsigned_arith_run.c $(BIN)/ww \
+		$(BIN)/w6c $(BIN)/w6c_ww $(BIN)/w6a $(BIN)/w6l \
+		$(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 $(BIN)/test_def_mangle_run: test/wcc/913_def_mangle_run.c $(BIN)/ww \
 		$(BIN)/w6c $(BIN)/w6c_ww $(BIN)/w6a $(BIN)/w6l \
 		$(LIB)/libwwrt.a | $(BIN)