The Belgian poet Marcel Broodthaers (1924-1976) supported himself for 40 years as a bookseller before deciding on a new career as an artist. In 1964, he turned some unsold poetry books into a sculpture, and instantly had a debut solo show. Four years later, he appointed himself director of a fictional art museum — his own. Now comes a belated and woozily perplexing first New York survey of one of Europe’s most influential 20th-century trickster-artist-poets, along with a complementary showcase, “Marcel Broodthaers: Écriture,” at Michael Werner Gallery on the Upper East Side.