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.
