[document parsing]: When tag declaration (but not definition!) 
is part of the decl-specifier-seq of some other declaration, 
it doesn't get comment. // rdar://12390371


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179722 91177308-0d34-0410-b5e6-96231b3b80d8