[CMake] Multiple library configurations with the same output name

[Alexey Livshits]

> Usually there are 2 ways: 1) put them into separate directories (like Debug
> and Release), probably specifying different output directories  or 2) use
> different file names, say adding suffixes like D, or d8.
> BTW, what's the point to have different configurations in the same workspace
> (do you really still use VC6?) in different projects? Usually for Visual
> Studio configuration is coded into output directory path using macros like
> $(Configuration), so resulting binaries are put into different dirs. And you
> have to build twise to get all configurations.
> Why do they required to have the same name? May be you're trying to solve
> wrong problem?

I don't need a new configuration like debug or release, but multiple
versions of our software. Same names for targets is a must.
CMake build process already works fine, I just try to optimize it.
Yes, I have to use VC6, because of legacy code.

-- 
BG,
Alexey