AST dumping: indicate the previous declaration for a redeclaration, and
indicate the semantic DC if it's not the lexical DC. In passing, correct
the ascii-art child marker for a child of a FriendDecl.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174570 91177308-0d34-0410-b5e6-96231b3b80d8