[Data formatters] Make NSSetM support both old- and new-style representation
[Data formatters] Make NSSetM support both old- and new-style representation

NSSetM has two in-memory representations depending on what Foundation version is in use.
This patch separates the two.

rdar://33057292

Differential Revision: https://reviews.llvm.org/D34821


git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@306773 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb