I know this is likely cumbersome to support as a case, as it requires to look at all the functions in the given unit to report it, but since GCC already reports unused functions in the unit I guess it is feasible.

Simple test case:

static unsigned int done = 0;

int main() {
  done = 1;

  return 0;
}

The warning works fine if done is function-static though.

Thanks,
Diego