However, whether applications rely on the std::bad_function_call vtable
being in the dylib is still controlled by the ABI macro, since changing
that would be an ABI break.
Also separate preprocessor definitions for whether to use a key function
and whether to use a bad_function_call-specific what message
(what message is mandated by LWG2233).
I think you had found a LWG issue that discussed this? If it is relevant, you could also add a link to it here.