flycheck in buffers with no file name

[mkanta]

Thank you for taking the time to improve Flycheck.

Checklist

• I have checked existing issues for potential duplicates before creating this one.
  I did some research on the error message created when using flycheck in a buffer with no associated file name and didn't
  find any feature requests to make this work.

Feature description

A clear and concise description of what you want Flycheck to do.
Flycheck should be able to run in buffers with no buffer-file-name, perhaps by not only creating a random directory name
for its /tmp directory but by also creating a random file name when buffer-file-name is nil. This would be a great improvement
for people who edit org-mode source blocks with org-edit-special.

Describe alternatives you've considered

A clear and concise description of any alternative solutions or features you've considered.
I tried to find a way to give the buffers created by org-edit-special a file name with the :file header, then looked at the
source code for org-edit-special. There seems to be no easy way to get buffers with filenames when using org-edit-special,
so it seems to me that flycheck generating random filenames might be the easier way to make this work.

Additional context

Add any other context or screenshots, mockups etc.