Suppres implicit-fallthrough from gcc 7
Some kind of comments are recognized by gcc7 but they are ignored with
-Wimplicit-fallthrough=5 and only attributes disable the warning.
Reviewed-by: Fabiano FidĂȘncio <fidencio@redhat.com>
(cherry picked from commit 2e505786d6d9d537f5b6631099862f6b93e2e687)