swift234

[IRGen] Don't emit ObjC class property metadata on old targets. (#2350)

The ObjC runtime on OS X 10.10 and older and iOS 9 and older can't
handle them, so for these targets, emit nil for all class property
lists.

It's a little unfortunate that this is target-dependent, but there's
not much we can do about it.

rdar://problem/25605427