wcc/cgen: #151 push all 3 header words for let-global slice/str by-value arg (wwstage)

A let-global slice or str passed by value as an argument was silently
field-dropped by wwstage: pushargsrev's global branch had only the #150-A
struct arm, and wwstage's nodeisslice/nodeisstr are local-keyed (false for
a global), so a global slice/str ident fell to the scalar single-PUSHQ,
pushing one of the three header words {ptr,len,cap} -> the callee read
garbage for .len/.cap. cstage was already correct.

wwstage-only, caller-side only (slice/str params already received
correctly). A global slice/str arm in pushargsrev, type-keyed on
tichase(arg.type_).kind, with two arms byte-matching cstage's two distinct
sequences -- str via cgslicehdr (CX-base, cgen.c:1866), slice per-word
(BX-base, cgen.c:9124). Gate is isletvar-only (a def has no name(SB)
holder; cstage const-folds it -- def-str/slice-by-value is the residual
task #21). cstage unchanged (w6c md5 unchanged); byte-id 990-997 8/8,
no lib pin flips. test/wcc/829 table-driven, byte-id per type.

Makefile

@@ -257,6 +257,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_alias_tuple_coerce \
 	  $(BIN)/test_str_eq \
 	  $(BIN)/test_overlong_arrlit \
+	  $(BIN)/test_slice_str_global_arg \
 	  $(BIN)/test_slice_str_global_zero \
 	  $(BIN)/test_slice_literal_global \
 	  $(BIN)/test_global_arr_elem_field \
@@ -707,6 +708,12 @@ $(BIN)/test_overlong_arrlit: test/wcc/828_overlong_arrlit.c $(BIN)/ww \
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_slice_str_global_arg: test/wcc/829_slice_str_global_arg.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_def_arr_infer_len: test/wcc/814_def_arr_infer_len.c $(BIN)/ww \
 		$(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
 		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \