[Bug c++/78283] -Wc++1z-compat warning is sticky

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78283

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 40011
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40011&action=edit
gcc7-pr78283.patch

Untested fix.