Add a new compiler setting that tells the JS build output to expect that the `locateFile` module hook will be used

This is an enhancement request.

I think this setting would reduce unnecessary JS code and complexity in the output that's left unused when `locateFile` is defined on the Module.

Perhaps it could be called `USE_LOCATE_FILE`, and a runtime error would be expected if `locateFile` was not defined.

/cc @RReverser