fix mishandling of the continuation-mark depth

When a chaperone-wrapped function leads to a slow-path tail
call, the continuation-mark depth can be made too deep when
resolving the slow tail call.

Closes #1265

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

@@ -2474,6 +2474,27 @@
   (test-wrapped wrapped-f)
   (test-wrapped wrapped2-f))
 
+;; ----------------------------------------
+;; Check that continuation-mark depth is handled
+;; properly when the JIT has to take a slow
+;; path for a tail call
+
+(let ()
+  (define (counter)
+    (let ([c 0])
+      (case-lambda
+        [() c]
+        [(x) (when (= c 1) (error 'fail)) (set! c (+ c 1)) #t])))
+
+  (for ([i 1000])
+    (let ([c (counter)])
+      (letrec ([f
+                (contract (-> any/c c)
+                          (λ ([x #f]) (if (zero? x) x (f (- x 1))))
+                          'pos
+                          'neg)])
+        (f 6)))))
+
 ;; ----------------------------------------
 
 (report-errs)

racket/src/racket/src/fun.c

@@ -3732,7 +3732,7 @@ static Scheme_Object *_apply_native(Scheme_Object *obj, int num_rands, Scheme_Ob
   obj = data->start_code(obj, num_rands, rands EXTRA_NATIVE_ARGUMENT);
 
   if (obj == SCHEME_TAIL_CALL_WAITING)
-    obj = force_values(obj, 1);
+    obj = scheme_force_value_same_mark(obj);
 
   MZ_CONT_MARK_STACK = old_cont_mark_stack;
   MZ_CONT_MARK_POS -= 2;