expander: fix higher-phase variable/syntax provide tracking

The check for whether a provided identifier is syntax or a variable
cuold incorrectly inspect a module that is not yet prepared for the
relevant phase.

pkgs/racket-test-core/tests/racket/module.rktl

@@ -3096,6 +3096,27 @@ case of module-leve bindings; it doesn't cover local bindings.
                exn:fail:contract?
                #rx"write: linklet is not serializable"))
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Make sure that re-exports at higher phases correctly track whether
+;; the export is a variable or syntax
+
+(for ([meta '(1 2)])
+  (define name (string->symbol (format "submodule-reexports-macro-at-meta-~a" meta)))
+  (eval `(module ,name racket/base
+           (module foo racket/base
+             (require (for-syntax racket/base))
+             (provide x)
+             (define-syntax x 5))
+           (module bar racket/base
+             (require (for-meta ,meta (submod ".." foo)))
+             (provide (for-meta ,meta x)))))
+
+  (namespace-require `(submod ',name bar))
+
+  (let-values ([(vals stxes) (module->exports `(submod ',name bar))])
+    (test 0 length vals)
+    (test 1 length stxes)))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (report-errs)

racket/src/expander/expand/binding-for-transformer.rkt

@@ -25,6 +25,7 @@
    [else
     ;; Use `binding-lookup` to both check for taints and determine whether the
     ;; binding is a transformer or variable binding
+    (namespace-visit-available-modules! ns (+ at-phase (module-binding-phase b)))
     (define-values (val primitive? insp protected?)
       (binding-lookup b empty-env null ns at-phase id))
     (not (variable? val))]))

racket/src/racket/src/startup.inc

@@ -73665,6 +73665,10 @@ static const char *startup_source =
 " #f)))"
 "(provided-as-transformer? b/p_0))))"
 "(let-values()"
+"(let-values((()"
+"(begin"
+"(namespace-visit-available-modules! ns_0(+ at-phase_0(module-binding-phase b_0)))"
+"(values))))"
 "(let-values(((val_0 primitive?_0 insp_0 protected?_0)"
 "(let-values(((b1_0) b_0)"
 "((empty-env2_0) empty-env)"
@@ -73673,7 +73677,7 @@ static const char *startup_source =
 "((at-phase5_0) at-phase_0)"
 "((id6_0) id_0))"
 "(binding-lookup52.1 #f #f b1_0 empty-env2_0 null3_0 ns4_0 at-phase5_0 id6_0))))"
-"(not(variable? val_0))))))))"
+"(not(variable? val_0)))))))))"
 "(define-values(layers) '(raw phaseless id))"
 "(define-values(provide-form-name) 'provide)"
 "(define-values"