I'm building mimalloc with -std=c++20 and as of Clang 14 the use of ATOMIC_VAR_INIT() causes a bunch of deprecation warnings (I didn't see these warnings previously with Clang 13). Right now the warnings are harmless (but annoying). I think this can be easily worked around by creating a new macro that expands to ATOMIC_VAR_INIT only if the value of __cplusplus is less than 2020.