I would expect it will work a lot better if you have one libc library per ABI, and link in the matching one to the executable (and the same for all your other libraries).

The only thing that may need to deal with multiple supported ABIs simultaneously is the kernel. But maybe kernels are using more explicit types?

Personally, I don't like to write code with int/long/etc. I want to know how many bits are in the thing, because it usually doesn't make sense for the program to sometimes have one number of bits, and sometimes another (pointer/memory offsets excluded).