Update Clang's SD-6 support to match N4200 (except for __has_cpp_attribute,
which we don't yet implement).


git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@221816 91177308-0d34-0410-b5e6-96231b3b80d8
Fix brace init of unions with unnamed struct members

The check for unnamed members was intended to skip unnamed bitfields,
but it ended up skipping unnamed structs. This lead to an assertion in
IRGen.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@221818 91177308-0d34-0410-b5e6-96231b3b80d8