Generate build script/Makefile that doesn't depend on node.

Most of the commands for building a project with `CommonML` are recorded into a simple list that can be dumped to a make file and executed without node.

There's only a couple of parts of `CommonML` that makes this difficult:
- We currently discover the location of dependencies by executing a `findlib` command during the build process that uses `execSync` on the fly to get the exact location on the machine for certain libraries. Instead, you could imagine dumping to an environment variable in the script such as:

```
$LOC_OF_MY_DEPENDENCY=`findlib blah blah`
ocamlc $LOC_OF_MY_DEPENDENCY/path/to/blah.cmo -o blah.exe
```

That would work because it doesn't require that the `build.js` actually ever receive the result of the `findlib` command.
- `build.js` is geared towards local development so it assumes other `CommonML` dependencies are pulled down to a specific location `node_modules`. If distributing to `opam` (which is the primary use case for generating a node-free build script/Makefile), you don't even recompile your dependencies. In that case, you'd want the ability to have `build.js` have a special mode that doesn't search for dependencies' source in `node_modules` and doesn't recompile them, instead it needs to do something else to find the generated libraries/artifacts and their locations. If `build.js` just supported this mode regardless of if you're generating a node-free Makefile, then there's nothing special we'd have to do to support Makefile generation. Think of this mode as "promoting" your `dependencies` field to `findLibDependencies`.

If these could be fixed, then it would be much easier to generate a `Makefile` that does not rely at all on node. That means you could use `CommonML` for development, but then publish to `opam` a version of your package that can work regardless of if the client has node installed. (You would also need to generate a separate `opam` `instal` file, `opam` file and a bunch of other stuff, but that's fairly easy.).

Start by reading build.js and the code that records build commands and dumps them to a Makefile. Trace the findlib execSync dependency lookup and the handling of dependencies from node_modules, then compare those paths with the opam publishing use case. Done means a generated Makefile can build without Node and can use installed dependency artifacts rather than recompiling source dependencies.

Written by the indexing model from the issue text.