I'm probably responding too late for OP who said they are boarding today, but for future readers... I would NOT check any medical equipment with the porters. I simply wouldn't trust how it's handled, even something that appears as durable as a manual wheelchair (though some transport chairs don't feel as rugged). Removable pieces (such as footrests) can come off and get lost, wheels or rims could be bent, even slightly, or other parts, rendering it challenging to use and you'd be stuck. I recommend you bring it onboard yourself. If the wheelchair isn't actually needed during the boarding process, use it to tote your carry-ons.
Enjoy your vacation!