Ondřej Surý authored May 14, 2019 and Ondřej Surý committed Feb 11, 2020

The ThreadSanitizer found several possible data races in our rwlock
implementation.  This commit changes all the unprotected variables to atomic and
also changes the explicit memory ordering (atomic_<foo>_explicit(..., <order>)
functions to use our convenience macros (atomic_<foo>_<order>).