[CMake] Support for languages without linking phase etc

[Ivan Chernetsky]

Hi there!

I've written almost all the .cmake files required to add Erlang
support, but when I was approaching completion, I realized--to be
honest, got confused by the fact that there is no linking phase. So
here is the question: what should CMAKE_Erlang_LINK_EXECUTABLE look
like? Or speaking more generally: what the overall strategy for adding
a new language that differs from the C/C++/etc in the build process?

I would be glad of any help.