wcc: reject module-scope alloc/call let initializers at check time

A module-scope let whose rhs runs code (alloc, call — peeled through
cast/?/! wrappers) emitted no DATAW slot: emit_lets' fold-fail
silently skipped the definition and every reference died at LINK
time with 'undefined reference', the one unacceptable failure mode
(rule 7). Hare's model rejects at check time (ref/harec/src/
check.c:4360 'Unable to evaluate initializer at compile time') and
routes runtime init through @init, which ww does not have — so both
frontends now reject at the declaration with identical wording.

alias_infptr_global flips compile->error as the alloc pin (its
letvartnode N_TPTR-over-N_TSTRUCT coverage lives on in the local
alias_infptr_{nest,slicecap} siblings); callinit_global_reject pins
the call shape. Corpus pin 1741/345/21/209/1166/3482.

cmd/wcc/check.c

@@ -3126,6 +3126,26 @@ check_file(Checker *c, Node *file)
 			if (t)
 				require_sized(c, t, d->pos, "a variable");
 			d->type = t;
+			/* A module-scope initializer must be link-time data:
+			 * an alloc/call rhs runs code, emit_lets' fold-fail
+			 * skipped the DATAW slot silently, and every
+			 * reference died at LINK time ("undefined reference")
+			 * — reject at the declaration instead (rule 7).
+			 * Hare rejects at check time too (ref/harec/src/
+			 * check.c:4360 "Unable to evaluate initializer at
+			 * compile time"); ww has no @init path. */
+			{
+				Node *r = d->rhs;
+				while (r != NULL && (r->kind == N_CAST
+				    || r->kind == N_TRYPROP
+				    || r->kind == N_TRYUNW))
+					r = r->lhs;
+				if (r != NULL && (r->kind == N_ALLOC
+				    || r->kind == N_CALL))
+					err(c, d->pos, "module-scope let %s: "
+					    "runtime initializer unsupported "
+					    "(alloc/call; rule 7)", d->str);
+			}
 			if (d->str && d->str[0]) {
 				Sym *prev = scope_lookup_local(c->cur, d->str);
 				const char *mod = decl_mod(file, d);