[Bug c/71719] [7 Regression] invalid set-but-not-used warning with vectors

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71719

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 38813
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38813&action=edit
gcc7-pr71719.patch

Untested fix.