Merge #10141 from blueyed/vim-8.0.1335

vim-patch:8.0.{1335,1339,1744}

src/nvim/testdir/test_writefile.vim

@@ -155,3 +155,15 @@ func Test_writefile_autowrite_nowrite()
   bwipe!
   set noautowrite
 endfunc
+
+func Test_writefile_sync_dev_stdout()
+  if !has('unix')
+    return
+  endif
+  if filewritable('/dev/stdout')
+    " Just check that this doesn't cause an error.
+    call writefile(['one'], '/dev/stdout', 's')
+  else
+    throw 'Skipped: /dev/stdout is not writable'
+  endif
+endfunc