Use bc-primitives for cr-target

The ehclib is compiled to target=cr when doing a make install. This fails because of undefined primitives used in uhcbase.

I don't know if the ehclib should actually be compiled to target=cr in the first place. If it should, then I guess the proper solution would be to know the final code-gen target(bc,jazy,js,...) for which cr should be generated, but I think this is not available at the moment.