fix clean-up handling for the main thread of a terminated place

This bug might be reposnible for the occassional crashes seen in
DrDr for the easter-egg test.

Merge to v6.0.1
(cherry picked from commit 83dcf446a3)

pkgs/racket-pkgs/racket-test/tests/racket/place-kill-unwind.rkt

@@ -0,0 +1,26 @@
+#lang racket/base
+(require racket/place)
+
+;; When a thread is killed during `directory-list`, there's
+;; a clean-up action attached to both the thread and its
+;; `dynamic-wind` chain (effectively). Check that only one
+;; of them runs, otherwise closedir() is called twice (and
+;; libc will typically detect a mistake and abort).
+
+(define (go)
+  (place
+   pch
+   (place-channel-put pch 'ok)
+   (let loop ()
+     (directory-list
+      (let-values ([(base name dir?)
+                    (split-path (collection-file-path "place.rkt" "racket"))])
+        base))
+     (loop))))
+
+(module+ main
+  (for ([i 25])
+    (printf "~a\n" i)
+    (define p (go))
+    (place-channel-get p)
+    (place-kill p)))

racket/src/racket/src/thread.c

@@ -4371,7 +4371,7 @@ static void escape_to_kill(Scheme_Thread *p)
   p->cjs.jumping_to_continuation = (Scheme_Object *)p;
   p->cjs.alt_full_continuation = NULL;
   p->cjs.is_kill = 1;
-  p->cjs.skip_dws = 0;
+  p->cjs.skip_dws = 1;
   scheme_longjmp(*p->error_buf, 1);
 }