[CMake] Chaneg executable extension

[Darko Miletic]

William A. Hoffman wrote:
> On windows, I think that is required.   For unix no extension is added.
> Exactly what are you trying to do?

By default it is expected to be .exe but in fact it can be any other 
extension. I need to produce executables with custom extension (.cgi).

I guess it is only possible to add custom post_build command that will 
rename executable.

Darko