cstage parse.c:1027 accepts `for ()` — N_FOR with a nil cond, no
for-else arm, no test emitted (an unconditional loop; a deliberate
Go-flavored ww divergence from Hare, original to the toolchain
import). The wwstage parser had no RPAREN early-out and rejected it.
Selfhost checker and cgen already nil-guard n.cond, so the parser arm
is the whole gap. Graduates the held e2e row (pin 1731/1157/3462).
Adjacent asymmetries left filed, not fixed here (rule 11): the brace
form `for { }`, the empty middle clause of the 3-clause form, and
the REVERSE case (wwstage accepts 2-clause `for (cond; post)` which
cstage rejects).
