When Clang encounters an already invalid class declaration, it can
emit incorrect diagnostics about the exception specification on
some of its members. This patch temporarily works around that
incorrect diagnostic.
The clang bug was introduced in r324062.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@324164 91177308-0d34-0410-b5e6-96231b3b80d8