Add synthetic children support for NSIndexPath

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@219852 91177308-0d34-0410-b5e6-96231b3b80d8
This should keep the non-Xcode-based builds happy

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@219853 91177308-0d34-0410-b5e6-96231b3b80d8