[Bug c/79153] -Wimplicit-fallthrough missed warning

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79153

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 42758
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42758&action=edit
gcc8-pr79153.patch

Untested fix.