CMake allows case sensitive folder naming when setting the folder property of a target. However MSBuild doesn't like that. It complains about having two projects named the same when trying to compile the solution and aborts. (Solution file error MSB5004: The solution file has two projects named "lldb tests")
In lldb/unittests/CMakeLists.txt a folder "LLDB tests" is defined and in lldb/lit/CMakeLists.txt a folder "lldb tests" is defined.
Renaming "lldb tests" to "LLDB tests" in lldb/lit/CMakeLists.txt fixes the problem.