JIDDA, Saudi Arabia — It is an architectural absurdity. Just south of the Grand Mosque in Mecca, the Muslim world’s holiest site, a kitsch rendition of London’s Big Ben is nearing completion. Called the Royal Mecca Clock Tower, it will be one of the tallest buildings in the world, the centerpiece of a complex that is housing a gargantuan shopping mall, an 800-room hotel and a prayer hall for several thousand people. Its muscular form, an unabashed knockoff of the original, blown up to a grotesque scale, will be decorated with Arabic inscriptions and topped by a crescent-shape spire in what feels like a cynical nod to Islam’s architectural past. To make room for it, the Saudi government bulldozed an 18th-century Ottoman fortress and the hill it stood on.