Pre-#40 wwstage's UNTYPED-float fold for `-2.5` was broken, so the
three f64-sign tests (fprintf_f64_neg, fprintf_f64_sign_plus,
asprintf_f64) used a `let nv: f64 = -2.5;` indirection to dodge it.
With #40 (session-3 commit 4d6a19f) landed, the wwstage variant-
widen N_UNARY-of-N_FLOATLIT fold renders the literal directly on
both stages. Indirection inlined; workaround comment blocks dropped.
Kept the sign-fold WHY in fprintf_f64_sign_plus (genuine semantic,
not a workaround note).
Hojun-Cho
a7700f201b