wwstage's tuple-parse loop checked the RPAREN-break at the top, so
`(a,)` parsed as a 1-element N_TUPLE and reached cgen — a silent
wrong-accept. A trailing comma is legal only after >=2 elements.
Align the loop order to cstage cmd/wcc/parse.c:552-558 (parse each
element before the RPAREN-break); `(a,)` now errors at the next
parseexpr, `(a, b)` / `(a, b,)` are unchanged. cstage already
rejected; this brings wwstage's w6c_ww parser into agreement.
Regen w6c/wwdump combined.ww (parser embeds in both). Valid-program
codegen unchanged → cs==ww byte-id gate stays green.
Hojun-Cho
6b7de54272