The `lazy-require' form expands to `define-runtime-module-path-index',
whch doesn't work right at phase levels other than 0. Work around the
problem by generating a submodule to hold the
`define-runtime-module-path-index' form.
This repair fixes `raco exe' on certain uses of `match', which in turn
uses `lazy-require' at compile time.
Also, use `register-external-module' to generate appropriate
dependencies on lazily loaded modules.
