Since r179585, __declspec(property) has gotten special treatment as an attribute where it is not processed as part of the typical Sema attribute functionality.  Specifying this attribute as being "ignored" because there is no sema handler for it as a Decl attribute, and no AST node generated for it.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189284 91177308-0d34-0410-b5e6-96231b3b80d8