[CMake] add_library without source code

[Matthias Gwein]

Hello!

I'm using cmake 2.8.2 and I'd like to build a library of libraries and  
i have no additional source code.
I tried something like that:

add_library(mylib )
target_link_libraries(mylib lib1 lib2)

But that doesn't work, because add_library needs at least a source file.

Is there any way to get that work, without creating a dummy source file?

Chears,
Matthias