[CMake] Multiple library configurations with the same output name

[Alexey Livshits]

Hello CMakers,
suppose I've got a library foo with tow configurations: foo_1 and
foo_2. Both versions should have the same output name: foo. The
problem is, the output directory for both ist the same, so the second
will overwrite the first.
What's the best way to organize it?

-- 
BG,
Alexey