Clean up the error recovery at the bottom of Sema::LookupMemberExpr. This

Clean up the error recovery at the bottom of Sema::LookupMemberExpr. This
mostly just shuffles various possibilities for recovery into a more
straightforward order, but also unifies a couple of diagnostics.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@126266 91177308-0d34-0410-b5e6-96231b3b80d8