OMake plugin has a bogus cmxs rule

[ivg]

The rule to build the %.cmxs files

    $(CMXSFILE): $(NATIVELIB) $(CLIB)
        $(OCAMLOPTLINK) -shared -cclib -L. -o $(CMXSFILE) $(NATIVELIB)

However, when cmxa is used, ocamlopt will only link those modules that are used. Since there are no other input files, the produced file is empty and totally useless.

Proposed solutions

1. Passing the -linkall option will resolve this issue and the cmxs file will have the same units as the cmxa file.

2. Alternatively, the cmxa file could be defined the same as cmxa rule, i.e., to build the output from the cmx files (and ofiles).

The former solution is easier to implement, the latter provides more opportunities for parallelization (cmxs and cmxa could be built in parallel), but at the cost of slightly more complex rule.

I can PRovide either solution so if you have any preferences I'm interested to know.