When parsing ignored attribute arguments, presuming the first argument is an unresolved identifier the same way that we do for unknown arguments. This resolves PR18075, where we regressed the handling of OpenBSD's bounded attribute.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@196387 91177308-0d34-0410-b5e6-96231b3b80d8