NEWTOWN SQUARE, Pa — For the past decade or so, the three most entertaining venues in golf have been Augusta National, the Old Course at St. Andrews, and Rory McIlroy’s head. Spend a little time inside any of them, and you could feel the game’s history and ride its ups and downs. That is why this week’s PGA Championship is so interesting for McIlroy: Whatever the weather at Aronimink, the (metaphorical) wind is blowing in the right direction. The second half of his career began this year, and McIlroy is well-positioned to win any major he enters. He is as talented and skilled as anybody in the world, and he has found the sweet spot between freedom and focus . McIlroy has already won two PGA Championships, in 2012 and 2014, and this has always been the major he is most suited to win. Scores tend to be low, and while the trophy is the heaviest, the weight of history is the lightest.…