Entertainers can be extremely needy people, and none more so than standup comedians, who both mine and risk personal humiliation in the pursuit of that instant gratification provided by an audience’s laughter and applause. Yet few high-profile comics acknowledge their thirst for affirmation, or the past and ongoing challenges informing it, as transparently or relentlessly as Gary Gulman does in his new one-man show, “Grandiloquent.”