This is the script I use to build all the native and cross targets that
musl-cross-make currently supports. You should just be able to do:

  git clone https://github.com/richfelker/musl-cross-make
  cd musl-cross-make
  ~/mcm-buildall.sh

And then wait a long time and the result should wind up in "output".

I'm still testing to make sure this can build all the root filesystems
and kernels (teaching my https://github.com/landley/mkroot to do kernels).

Rob