Escape hell, and how to escape it

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3

Found this in the docs for target_compile_options: https://cmake.org/cmake/help/latest/command/target_compile_options.html#option-de-duplication

Building a list of options with it, like so, works:

      if(EXISTS "${MODULE_SOURCE_DIR}/module.modulemap")
        list(APPEND LOCAL_CXX_FLAGS "SHELL:-Xcc -fmodule-map-file=${MODULE_SOURCE_DIR}/module.modulemap")
      endif()