Dual ABI support in a single file library? What's the easiest/best practice way?

• How can we compile a shared library to support both ABIs in a single .so file using Modern CMake (>3.4)?

If this is not possible, what's the best practice for that? I'd like to avoid hard-coded and custom code to keep the maintenance straightforward.

I found this link but it requires to change the code and uses gcc only: http://kayari.org/cxx/dualabi.html

Reason: My users have Centos 7 (old ABI exclusively) and Centos 8 (both ABI). The size of the library isn't important as long as the performance doesn't change.

Targets: gcc and cmake