I'm just going through the motions. GCC has FSF GNAT which I wan't on macOS, but in order to compile gcc with ada support you need to have GNAT already.

So, what I'm doing now is: download GPL GNAT from Ada Core here: http://libre.adacore.com/download/ and build your gcc, as usual, with ada support from that. Then you can use FSF GNAT gcc. You can even compile again with FSF gcc to make it double sure it's working.

Apparently, FSF GNAT version is what you want in order to make commercial software since it has a runtime license, which Ada Core version doesn't. You would have to pay for Pro version. Someone correct me if I'm wrong.

GNAT