Performance improvements to the IsObjCNil () - we only try to resolve the value if the variable under consideration truly is an “Objective-C thing”
This also changes the ClangASTContext to make sure that id is correctly marked as being such an ObjC thing

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@177203 91177308-0d34-0410-b5e6-96231b3b80d8