cs: fix touch on a future blocked on a fsemaphore

Relevant to #2957

pkgs/racket-test/tests/future/fsemaphore.rkt

@@ -0,0 +1,18 @@
+#lang racket
+
+;; Check `touch` on a future blocked on an fsemaphore
+
+(define mutex (make-fsemaphore 1))
+
+(define futures
+  (for/list ([i 10])
+    (future
+     (lambda ()
+       (fsemaphore-wait mutex)
+       (println (add1 i))
+       (fsemaphore-post mutex)))))
+
+(void
+ (map sync
+      (for/list ([f (in-list futures)])
+        (thread (lambda () (touch f))))))

racket/src/thread/future-object.rkt

@@ -17,7 +17,7 @@
                  [prev #:mutable]   ; queue previous
                  [next #:mutable]   ; queue next
                  [results #:mutable]
-                 [state #:mutable]  ; #f (could run), 'running, 'blocked, 'done, 'aborted, 'fsema, or future waiting on
+                 [state #:mutable]  ; #f (could run), 'running, 'blocked, 'done, 'aborted, 'fsema or box, or future waiting on
                  [dependents #:mutable]) ; futures that are blocked on this one
   #:authentic
   #:reflection-name 'future)

racket/src/thread/future.rkt

@@ -287,7 +287,7 @@
         (lock-release (future*-lock f))
         (touch s)
         (touch f)])]
-    [(box? s) ; => dependent on fsemaphore
+    [(or (box? s) (eq? s 'fsema)) ; => dependent on fsemaphore
      (cond
        [(current-future)
         ;; Lots to wait on, so give up on the current future for now