https://github.com/stenzek/duckstation/blob/47e8d90e25c5857bcfd4604dee6d9c7ff8255314/CMakeModules/DuckStationBuildSummary.cmake#L32-L36

  # Stop users being silly.
  if("${CMAKE_INSTALL_PREFIX}" MATCHES "^/usr")
    message(FATAL_ERROR "You are trying to install DuckStation into a system directory, this is not supported. Please use a different CMAKE_INSTALL_PREFIX.")
  endif()
endif()

I'm too silly for you.

Culmination of duckstation repackaging: https://github.com/NixOS/nixpkgs/pull/433242

^If anyone wishes to have a duckstation derivation that is up-to-date with upstream development. I'm not sure if this should be merged, but I thought it would be productive to submit anyways.