Mark seed_seq default constructor and size() as noexcept. This is implied, but not required by LWG issue 2180

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@193227 91177308-0d34-0410-b5e6-96231b3b80d8
Update status of issues

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@193228 91177308-0d34-0410-b5e6-96231b3b80d8