Pretty electic mix, based on these lists (doesn't factor in clock-wise/counter-cw routing):
Loop:
ANGC
Shinnecock
Oakmont
WF West
Seminole
Southern Hills
Oakland Hills
Five Farms
Oak Hill East
Quaker Ridge
Canterbury
Scioto
Colonial
Interlachen
Cherry Hills
Riveria
Pasa
Prairie Dunes (sort of; don't know that Press had much choice of routing w/ new nine....)
Non-looped:
Cypress Point
Baltusrol Lower
TCC (Championship routing
NGLA
Olympic
Pinehurst #2
Merion East
Pine Valley
Pebble Beach
Cascades
Chicago
Medinah #3 (had to throw in...)
Admittedly, as Pat says, some sites may only be suitable for an out-and-back, narrow routing (Pebble among them?). But the above lists don't seem to indicate that golden-age architects specifically routed courses in a looped or non-looped fashion, to take into account wind variation. Just based on maps and other visuals I've seen of these courses, one could have certainly designed many of the looped courses in a non-loop routing, and the non-looped ones in a loop. Whether they'd be as good, or not, or better, is another matter.
One other (perhaps minor) point -- the nine-hole, two-loop nature of a course's routing is a pretty arbitrary thing, if what you're leaving from and returning to is the clubhouse. It would seem difficult, for instance, to do two loops at Merion East, given that 11 holes are on one side of the road opposite from the clubhouse. But then you could move the clubhouse to somewhere around the 10th green, 1st green and 2nd tee and have your two loops.