[Bug sanitizer/68260] false positive with tsan

[dvyukov at google dot com]

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

--- Comment #7 from Dmitry Vyukov <dvyukov at google dot com> ---
I looked at the patch, but I am unqualified to review it. The test looks good
to me. +Yuri