ffi/unsafe: fix tauint handling in define-fun-syntax

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

@@ -148,6 +148,9 @@
   (check t 'd 16)
   (check t '(a b) 3))
 
+;; Make sure `_box` at least compiles:
+(test #t ctype? (_fun (_box _int) -> _void))
+
 (define-cstruct _ic7i ([i1 _int]
                        [c7 _c7_list]
                        [i2 _int]))

racket/collects/ffi/unsafe.rkt

@@ -351,7 +351,7 @@
          [else (set! keys (cons (cons key val) keys))]))
      (let loop ([t (disarm orig)])
        (define (next rest . args) (apply setkey! args) (loop rest))
-       (define (rearm e) (syntax-rearm e orig))
+       (define (rearm e) (syntax-rearm e orig #t))
        (syntax-case* t
            (type: expr: bind: 1st-arg: prev-arg: pre: post: keywords: =>)
            id=?