An include for a rather obscure boost preprocessor header has been added by the IWYU sweep, to over 1500 c++ source files.

#include <boost/preprocessor/control/iif.hpp>

I don't really understand why IWYU would do this to a file like
"src/mongo/db/commands/server_status_metric.h", which doesn't have any macros inside it at all. It seems like IWYU made a mistake here and it should be undone.

I think maybe one of the other headers needs something from the iif.hpp header and IWYU didn't resolve that dependency appropriately.