build: add support for releasing cross-compiled debug binaries
build: add support for releasing cross-compiled debug binaries

sh/cross can now be invoked as follows:

sh/cross urbit linux64
sh/cross urbit darwin

sh/cross urbit-debug linux64
sh/cross urbit-debug darwin

urbit/urbit,ngzax/urbit,jfranklin9000/urbit,jfranklin9000/urbit,urbit/urbit,jfranklin9000/urbit,urbit/urbit,ngzax/urbit,jfranklin9000/urbit,ngzax/urbit,ngzax/urbit,jfranklin9000/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,jfranklin9000/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit,jfranklin9000/urbit,urbit/urbit