PR15300: Support C++11 attributes on base-specifiers. We don't support any such
attributes yet, so just issue the appropriate diagnostics. Also generalize the
fixit for attributes-in-the-wrong-place code and reuse it here, if attributes
are placed after the access-specifier or 'virtual' in a base specifier.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175575 91177308-0d34-0410-b5e6-96231b3b80d8