Comment by delta_p_delta_x

A considerable number of C++ libraries are header-only, so having this macro defined is the onus of the libraries' consumers, rather than just the package managers'.

Also, I mentioned no libc equivalent, and that remains true. Regardless of the libc distribution (glibc, musl, BSD, macOS libSystem), none of them have a debug mode in the vein that Windows UCRT does.