swift234

Introduce a swift-specific alias analysis pass that knows that retain/release/alloc
don't mod/ref any state to swift code.  This allows the general LLVM optimizer to be
*much* more aggressive.  For example, on swift.swift, GVN deletes 15% more instructions,
jump threading folds 2.4X more terminators, SCCP removes 3.3X more instructions, and 2
more retain/release pairs are removed by the ARC optimizer.


Swift SVN r2113