Automake used to support an obscure feature called multilibs. This feature is now deprecated, and will be removed in the next major Automake version. Still, its implementation will remain available in the contrib/ directory of the Automake distribution, so it should be very easy for motivated users to continue to use it in their projects, if they really need to.
A multilib is a library that is built for multiple different ABIs at a single time; each time the library is built with a different target flag combination. This is only useful when the library is intended to be cross-compiled, and it is almost exclusively used for compiler support libraries.