A mentally ill veteran whose hoarded the body of a dead dog, pieces of bombs and an arsenal of weapons on his Maryland property — on which multiple fires have broken out — is being used by far-right activists to break down American gun protection laws, according to a new investigative report. Donald Willey — a veteran diagnosed with ADHD who admitted to debilitating depression on an episode of “Hoarding: Buried Alive” — has become the poster child of the Second Amendment Foundation group’s fight against red-flag laws in nearly two dozen states, Rolling Stone and nonprofit newsroom the Trace re…