[Bug sanitizer/68260] false positive with tsan

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68260

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 39573
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=39573&action=edit
gcc7-pr68260.patch

Untested fix.