Automatically set ETL_HAS_ATOMIC if __STDC_NO_ATOMICS__ defined by compiler. (#624)
Automatically set ETL_HAS_ATOMIC if __STDC_NO_ATOMICS__ defined by compiler. (#624)

Reference: https://en.cppreference.com/w/c/atomic

Co-authored-by: Jeremy Erdmann <87a3bd50a78cc4bce5ba4f82af4f37e210cb1b44@millerwelds.com>
ETLCPP/etl,ETLCPP/etl,ETLCPP/etl,ETLCPP/etl