WSL: Disable read-only bind mount

When re-mounting a bind mount read-only WSL fails with EBUSY if there
are any outstanding writable file-descriptors anywhere on the filesystem
(even outside the bind-mount). This makes read-only bindmounts fail
most of the time (for example in flatpak due to writable /var/tmp files).

For now we just disable read-only.

Author: alexlarsson

bind-mount.c

@@ -408,6 +408,11 @@ bind_mount (int           proc_fd,
 
   assert (path_equal (mount_tab[0].mountpoint, resolved_dest));
   current_flags = mount_tab[0].options;
+
+  /* WSL: Any writable fd open on the same fs that the bindmount is on will block the readonly
+     bind mount with EBUSY, so we ignore it for now. */
+  readonly = FALSE;
+
   new_flags = current_flags | (devices ? 0 : MS_NODEV) | MS_NOSUID | (readonly ? MS_RDONLY : 0);
   if (new_flags != current_flags &&
       mount ("none", resolved_dest,