There are essentially 3 flavors of haiku. Gcc2 for beos compatibility, gcc8 32 bit and gcc8 64 bit. LLVM I think can also compile the source but is not an official build as of now. I am a casual lurker so my details should be taken with a grain of salt.

I actually checked after I wrote that comment -- Haiku does ship numpy in their repos. That seems to be one of the harder Python libraries to get working, so they must be doing something right.