No, they didn't.
McDonald's does not, and never has, funded the IRA. This story is based on an old urban myth that dates back to the 1970's when McDonald's first opened up shop in the UK. The payslips used for UK staff at that time were imported from the USA, and included printed reference to the American equivalent to NI pension contributions - the 'Individual Retirement Account' - or 'IRA' for short. The rumour that McDonald's donated to the IRA terrorist group arises from this misunderstanding.