Hojun-Cho
c814856550
Mirror cstage's C-variadic call handling in the ww self-host: parse a bare `...` param (decl.ww), skip param-keyed desugar for it to avoid a nil-deref (check.ww), and emit AL = XMM-reg count plus CVTSS2SD promotion of f32 args in the variadic tail (cgenutil.ww, cgenexpr.ww). Closes the cat-A wwstage silent miscompile (AL=0, unpromoted f32 tail). Parse/check/cgen are one atomic align-up (parse alone miscompiles, so not bisect-splittable). 989_ffivariadic now runs dual-stage (cstage ww + wwstage ww_ww), 12/12; w6c==w6c_ww byte-identical. Byte-id alone is blind here (the bootstrap calls no float-bearing C variadic), so the ww_ww runtime rows are the real net.