Varying cxxSettings defines in SPM

I have a C++ library that has multiple variants/tiered capabilities. This is controlled by preprocessor defines that can enable/disable capability sets.

I'm trying to map this into an SPM Package but am having trouble. At first I tried multiple targets, but SPM says that my targets have overlapping sources.

Is there any way to have a clear outputs in an SPM project that are the same source files with different pre-processor configurations? If not, is there any way to inject those preprocessor flags from a hosting Xcode project?

The only way I know of is to have symlinks to the same source files inside the different targets.