<rdar://problem/13119621>

Make dynamic type detection faster by using the AST metadata to help out and allow us not to complete types when we don't need to.

After running "purge" on a MacOSX system, the Xcode variables view now populates more than 3x faster with this fix.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@176676 91177308-0d34-0410-b5e6-96231b3b80d8