[Bug sanitizer/63559] -fsanitize=thread sets no preprocessor flags

[rogero at howzatt dot demon.co.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63559

--- Comment #2 from Roger Orr <rogero at howzatt dot demon.co.uk> ---
Hi Dmitry,
the false positives I've investigated seem to be down to spin-locked queues and
use of intel tbb concurrency data structures - AFAICT we don't have source for
the latter so I wouldn't expect tsan to resolve either of them.