scripts/apibuild.py did not consider exporting external variable's
comments into the XML API. This commits fixes that.
Noe that the way that CParser is designed, it is currently possible to
lose a parsed comment when parsing other fields as self.comment in
several places. I've added a comment to highlight this.
Signed-off-by: Victor Toso <victortoso@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>