Parallel Build: fix make-directory race condition

collects/setup/scribble.rkt

@@ -19,6 +19,7 @@
          scribble/html-properties
          scribble/manual ; really shouldn't be here... see dynamic-require-doc
          scribble/private/run-pdflatex
+         unstable/file
          (prefix-in html: scribble/html-render)
          (prefix-in latex: scribble/latex-render))
 
@@ -682,7 +683,7 @@
     (unless latex-dest
       (let ([dir (doc-dest-dir doc)])
         (if (not (directory-exists? dir))
-          (make-directory dir)
+          (make-directory*/ignore-exists-exn dir)
           (for ([f (directory-list dir)]
                 #:when
                 (and (file-exists? f)
@@ -781,7 +782,7 @@
 (define (write- latex-dest vers doc name data)
   (let* ([filename (sxref-path latex-dest doc name)])
     (when (verbose) (printf " [Caching to disk ~a]\n" filename))
-    (make-directory* (doc-dest-dir doc))
+    (make-directory*/ignore-exists-exn (doc-dest-dir doc))
     (with-compile-output filename 
       (lambda (out tmp-filename)
         (write-bytes (s-exp->fasl (append (list (list vers (doc-flags doc))) data)) out)))))