w6c+wwstage: wwstage alias-aggregate-return loud-stop + #276 citations (#272 review)

Review fixes for the #272 fold (reviewer272b gate; rob+ken ruling). Bundled
because the wwstage catch-all message carries the citation and the combined.ww
regen covers both .ww edits.

- wwstage cgreturn close-by-construction catch-all keyed on the SYNTACTIC
  return-type node (N_TARRAY / N_TNAME+structlookup), so a named-alias
  aggregate return type (type a=[N]T / type a=struct) bypassed both the
  handling arms AND the loud-stop, falling to the scalar default = silent
  segfault/truncation; cstage (type_chase_named at all 4 N_RETURN sites)
  stayed correct. Re-key the catch-all on the RESOLVED tinfo (chase
  TY_NAMED -> TY_ARRAY/TY_STRUCT) so wwstage LOUD-STOPS (rule 7) instead of
  miscompiling. cstage stays correct; the full wwstage tinfo-kind dispatch
  (align UP, byte-id) is #277. Established wwstage-stricter divergence
  (cf #264), no bootstrap consumer (990-997 green).

- #276 citations at-site (both stages): the cstage >24B array-literal return
  loud-stop and the <=24B STRUCT global-receive residual now cite #276. The
  wwstage >24B array-literal routes through the tinfo-keyed catch-all
  (#272/#276/#277). Correction: ALL <=24B struct globals truncate
  symmetrically (byte-id-clean), not only float-bearing -- #276 broadened.

- Cosmetic: fix a double-encoded U+2264 (mojibake) in the cgen.c commit-2
  comment.

combined.ww regenerated (#110).

cmd/w6c/cgen.c

@@ -5693,13 +5693,19 @@ cgexpr(Cg *c, Node *n, Local *locals)
 				    && n->rhs && n->rhs->kind == N_CALL
 				    && n->op == TK_ASSIGN) {
 					/* #272: `g = f();` where g is a GLOBAL
-					 * aggregate ≤24B. The callee leaves the result
+					 * aggregate ≤24B. The callee leaves the result
 					 * in AX/DX/CX (#272 reg-return); the scalar IDENT
 					 * fall-through below would store only MOVQ AX,
 					 * g(SB) = the first word. The asm has no `g+8(SB)`
 					 * operand form, so LEAQ the symbol into DI and
 					 * store the full+tail words. Mirrors the str/slice
-					 * global arm above and the #220 sret-to-symbol path. */
+					 * global arm above and the #220 sret-to-symbol path.
+					 * #276: this arm is TY_ARRAY-only — a ≤24B STRUCT
+					 * global receive can be float-class (X0/X1, not
+					 * AX/DX/CX) so it stays at its pre-existing symmetric
+					 * fall-through; closing it needs struct_float_class
+					 * here. No consumer. Arrays are never float-class, so
+					 * AX/DX/CX is always correct for this arm. */
 					int sz = (int)lu->size;
 					cgexpr(c, n->rhs, locals);
 					ins2(c, A_LEAQ, masym(c, n->lhs->str), areg(D_DI));
@@ -9740,11 +9746,11 @@ cgstmt(Cg *c, Node *n, Local **locals, int *frame)
 						k += 1;
 					}
 				} else if (n->lhs->kind == N_ARRLIT) {
-					/* #272: a >24B array-literal return has no
-					 * consumer and the ptr-relative element fill
+					/* #272/#276: a >24B array-literal return has
+					 * no consumer and the ptr-relative element fill
 					 * is untested. Loud-stop (rule 7) rather than
 					 * fall to the scalar default. ≤24B is wired. */
-					fatal("#272: >24B array-literal return "
+					fatal("#272/#276: >24B array-literal return "
 					    "unsupported (rule 7, no consumer)");
 				} else {
 					/* #272: N_DOT / N_INDEX / deref — land the