[Bug sanitizer/78267] [7 Regression] libsanitizer breaks bootstrap on x86_64-apple-darwin16 at r241977

[m.ostapenko at samsung dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78267

--- Comment #8 from Maxim Ostapenko <m.ostapenko at samsung dot com> ---
(In reply to Dominique d'Humieres from comment #7)
> > Attaching untested fix.
> > Dominique, could you try it?
> 
> Allow for ~2 hours.

Or better Jakub's fix, it looks cleaner.