[cmake-developers] CMakeParseArguments: Do not skip empty arguments

[Daniele E. Domenichelli]

Hello,

I updated the CMakeParseArguments_EmptyArgs topic, so that it will work
properly with cmake 3.0.0 (after the branch set_emptyvar_PARENT_SCOPE
topic is merged) and with older releases (I had to add a workaround for
that)

Can you please review it?

Thanks!

 Daniele