[CMake] Release and Debug build for same source folder?

[motes motes]

I would like to create a Release and Debug Build for my source files.
Currently I have been able to make both build types separately but it
would be nice to not have duplicated source files.

My source files depends on ITK and Elastix. I have therefore made both
a Debug and Release build for ITK and Elastix.

Now in my source folder I need to create two CMakelist.txt files. One
that uses the ITK and Elastix Release build and another that uses the
Debug builds. But how do I make CMake use the right CMakeList.txt
file?

Or am I doing it wrong?