LOS ANGELES—Gavin MacLeod, the veteran supporting actor who achieved stardom as Murray Slaughter, the sardonic TV news writer on “The Mary Tyler Moore Show,” before going on to even bigger fame as the cheerful Capt. Stubing on “The Love Boat,” has died. He was 90. MacLeod died early Saturday, his nephew, Mark See, told Variety. MacLeod’s health had been poor recently but no cause of death was given, the trade publication reported. Known to sitcom fans for his bald head and wide smile, MacLeod toiled in near anonymity for more than a decade, appearing on dozens of TV shows and in several movies before landing his “Mary Tyler Moore” role in 1970. He had originally tested for Moore’s TV boss, Lou Grant, a part that went to Ed Asner. Realizing he wasn’t right for playing the blustery, short-tempered TV newsroom leader, MacLeod asked if he could try instead for the …