Is there some sort of feature-test macro that client code can use to determine whether it is being compiled against libc++abi?
I see that there is
#define _LIBCPPABI_VERSION 1002
in the libc++abi-provided cxxabi.h. It would apparently happen to help tell libc++abi from libstdc++/libsupc++ (where _LIBCPPABI_VERSION is left undefined after #include <cxxabi.h>), but I'm not sure whether that's by design or by accident?