swift234

Teach the LLVM level ARC optimizer about swift_fixLifetime.

This includes:

1. Teaching SwiftAA that swift_fixLifetime does not affect loads, stores of pointers.
2. Teaching SwiftARCExpand to remove swift_fixLifetime.
3. Teaching SwiftARCOpts that it can move retains but not releases over
swift_fixLifetime.

At -O I get the following % speedups > 10%.

InsertionSort:|%29.73
ImageProc:|||||%23.97
RC4:|||||||||||%19.46
PrimeNum|||||||%18.10
Ary||||||||||||%14.09
Ary2|||||||||||%13.16

<rdar://problem/18685662>

Swift SVN r22814