Check other built-in ioengines for struct ioengine_ops name

[vincentkfu]

When fio loads an external ioengine it needs to find a struct ioengine_ops. It first checks for a symbol matching the ionegine's name and if that fails for an ioengine symbol. If the ioengine has a symbol matching its name that is not struct ioengine_ops then the ioengine cannot be loaded as an external ioengine.

We should check existing built-in ioengines to see whether they have symbols matching their names that are not struct ioengine_ops and rename them if so.

Or we could add a magic number to struct ioengine_ops and if it does not match for the symbol matching the ioengine name try the ioengine symbol.

Background: https://github.com/axboe/fio/issues/1874