emitter: Put all o_build_* stuff into new write_build_op.
emitter: Put all o_build_* stuff into new write_build_op.

There were two areas using o_build_list, and one area using o_build_hash. These
three places used near-identical code. This removes that in favor of one call
that takes a fair number of params.

This moves all build stuff into one place, which is very nice.

boardwalk/lily,boardwalk/lily,crasm/lily,crasm/lily,crasm/lily