add_definitions and include_directories don't operate on a by-target basis, they act on a
by-directory basis (i.e. if we defined two targets, A and B, in this CMakeLists file, add_definitions
would add the definitions to the COMPILE_DEFINITIONS directory property which both A and B would
implicitly use).
The same idea applies to include_directories, only it appends to the INCLUDE_DIRECTORIES directory
property.
Instead, specify these on the target to keep scope as narrow as possible.
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