Fix cmake error: Mixed styles of target_link_libraries signatures
Plain and keyword target_link_libraries signatures cannot be mixed.
Complete error message:
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CMake Error at src/testutils/CMakeLists.txt:76 (target_link_libraries):
The keyword signature for target_link_libraries has already been used with
the target "testutils". All uses of target_link_libraries with a target
must be either all-keyword or all-plain.
The uses of the keyword signature are here:
* src/testutils/CMakeLists.txt:72 (target_link_libraries)
-- Configuring incomplete, errors occurred!
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See: https://cmake.org/cmake/help/v3.0/policy/CMP0023.html