[analyzer] Merge RegionStore's KillStruct and CopyLazyBindings: BindAggregate.
[analyzer] Merge RegionStore's KillStruct and CopyLazyBindings: BindAggregate.

Both methods need to clear out existing bindings and provide a new default
binding. Originally KillStruct always provided UnknownVal as the default,
but it's allowed symbolic values for quite some time (for handling returned
structs in C).

No functionality change.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@161637 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang