Enable cpp-only builds in .mad directories

[valassi]

Minor reminder: when CUDA is missing, the cudacpp Makefile knows how to do cpp-only builds, but the fortran makefile not yet.

I had added a hack here, but it is ugly and does not work when CUDA is there (gmadevent is not built)

valassi@215ef2a

[valassi]

This is an old issue. It is essentially fixed, if not already earlier, at least in PR #798 where separate targets are built.