I am using TagLib as a static library with Visual Studio using CMake with

find_package(TagLib CONFIG)

This works well, but I still have to remember to manually set the TAGLIB_STATIC compile definition. I think instead of having

in your CMakeLists.txt, it should be

if(NOT BUILD_SHARED_LIBS)
  target_compile_definitions(tag PUBLIC TAGLIB_STATIC)
endif()

This should also put the definition in the installed taglib-targets.cmake file, so that when imported, the project using TagLib automatically has the correct compile definition.