[arcmt] In ARC default for properties is 'strong' so just remove a 'retain' if possible,
instead of changing it to 'strong'. rdar://9984862.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@142304 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed