The IRA always said that their 'terrorist campaign', or in their words 'struggle', would cease once they were satisfied that their legitimate demands had been recognized.
That's what Corbyn always said and probably what Gaddafi said too.
I suppose you can spin it that negotiating with the IRA and agreeing to many of their demands with the IRA leader ending up as Deputy First Minister of Northern Ireland doesn't count as 'supporting the IRA'. If that makes you feel good while still allowing you to criticize Corbyn but not the people who did the actual negotiation then by all means carry on.
Isn't the IRA official stance that they don't even recognize the current Irish Republic because it was not properly constituted from the start but started out as a sort of British dominion? Or am I confused with another xIRA?
Second, it's not the IRA leader but the Sinn Fein leader who ended up as Deputy First Minister and who has (im)plausible deniability that he was in the IRA command structure.
Third, most importantly, I think there's a considerable difference between negotiating with the IRA and praising their actions. The first is a clear necessity to bringing an end to the conflict. You have to get them on-board for the violence to stop, or at least a large enough fraction that the break-aways will be ineffectual. The second condones violence against the state you aspire to serve as a politician. And even if Corbyn himself made wishy-washy statements like that he didn't condone all their actions, he associated with people who clearly applauded the Brighton bombing, while he was already an MP. That's an incredibly stupid thing to do, it will come to haunt you.
Likewise, there's nothing wrong, IMHO, with talking with the
Peace and Prosperity Party Hamas; you'll need to get them on-board somehow for a lasting peace in the Middle East. But it seems Corbyn associates in doing so with people who express admiration for Hamas. He'd better leave the talking with Hamas to his
vaunted predecessor who'll bring peace any time now as special envoy of the Quartet.
Of course, all such things can be overlooked when you show leadership and have charisma. See, e.g., Joschka Fischer: he withered the allegations that he had thrown stones at the police (true), that he had given bed and breakfast to a RAF terrorist (true), and undoubtedly many more but I don't read Bild; but he kept the party together in the fractuous disputes between "realos" and "fundis" and managed to get his party into government (*). But Corbyn has the charisma of a damp towel and has increased the divisiveness within his party.
And on top of all his associations with the wrong people, Corbyn seems to never miss an opportunity to miss an opportunity to take the government to task (no, that sentence is not a typo!). All in all, it seems to me that, apart from the question whether Corbyn is too left or not left enough, he's just not fit to lead his party. Labour better dump him before the 2020 elections.
(*) And then, as leader of an avowed pacifist party, and as foreign minister, scrambled his state into its first war ever. Ahem.