This supports common coding patterns. The GCC C front end before
version 7 rejects the may_alias attribute on a struct definition
if it was not present in a previous forward declaration, so this
attribute can only be conditionally applied.
This implements the spirit of the change in Austin Group issue 1641.
Suggested-by: Marek Polacek <polacek@redhat.com>
Suggested-by: Jakub Jelinek <jakub@redhat.com>
Reviewed-by: Sam James <sam@gentoo.org>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
8d7b6b4cb2