expander: treat unbound and top-level-bound as free-identifier=?

Restores quetionable but traditional behavior.

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

@@ -1692,6 +1692,20 @@
 (require (for-meta 4 racket/base))
 (test #t free-identifier=? #'lambda #'lambda 0 4)
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Unbound and bound at toplevel are equivalent by `free-identifier=?`
+
+(test #t free-identifier=? #'defined-at-the-top-level (datum->syntax #f 'defined-at-the-top-level))
+(define defined-at-the-top-level 'yep)
+(test #t free-identifier=? #'defined-at-the-top-level (datum->syntax #f 'defined-at-the-top-level))
+
+(define-syntax-rule (define-defined-at-the-top-level)
+  (begin
+    (define defined-at-the-top-level 10)
+    (test #f free-identifier=? #'defined-at-the-top-level (datum->syntax #f 'defined-at-the-top-level))))
+(define-defined-at-the-top-level)
+(test #t free-identifier=? #'defined-at-the-top-level (datum->syntax #f 'defined-at-the-top-level))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;  certification example from the manual
 

racket/src/expander/syntax/binding.rkt

@@ -43,14 +43,20 @@
 ;; ----------------------------------------
 
 (define (free-identifier=? a b a-phase b-phase)
-  (define ab (resolve+shift a a-phase #:unbound-sym? #t))
-  (define bb (resolve+shift b b-phase #:unbound-sym? #t))
+  (define ab (toplevel-as-symbol (resolve+shift a a-phase #:unbound-sym? #t)))
+  (define bb (toplevel-as-symbol (resolve+shift b b-phase #:unbound-sym? #t)))
   (cond
    [(or (symbol? ab) (symbol? bb))
     (eq? ab bb)]
    [else
     (same-binding? ab bb)]))
 
+(define (toplevel-as-symbol b)
+  (if (and (module-binding? b)
+           (top-level-module-path-index? (module-binding-module b)))
+      (module-binding-sym b)
+      b))
+
 (define (same-binding? ab bb)
   (cond
    [(module-binding? ab)