Diagnose dll attribute on member of class that already has a dll attribute

Differential Revision: http://reviews.llvm.org/D3973

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@209954 91177308-0d34-0410-b5e6-96231b3b80d8
PR12961 - Extend DR532 to cover C++98/03.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@209955 91177308-0d34-0410-b5e6-96231b3b80d8
Use make_error_code in preparation for making errc an enum class.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@209956 91177308-0d34-0410-b5e6-96231b3b80d8