src/Pure/Admin/build_cygwin.scala

--- a/src/Pure/Admin/build_cygwin.scala	Mon Feb 04 15:45:40 2019 +0100
+++ b/src/Pure/Admin/build_cygwin.scala	Mon Feb 04 16:01:44 2019 +0100
@@ -35,7 +35,7 @@
 
         File.write(cygwin_isabelle + Path.explode("cygwin_mirror"), mirror)
 
-        File.executable(cygwin_exe)
+        File.set_executable(cygwin_exe, true)
         Isabelle_System.bash(File.bash_path(cygwin_exe) + " -h </dev/null >/dev/null").check
 
         val res =