Implement change #4 of P1466: Change weekday to accept both 0 and 7 as Sunday. Add accessors 'c_encoding' and 'iso_encoding' to provide different interpretations of the weekday. Remove 'operator unsigned'

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@366981 91177308-0d34-0410-b5e6-96231b3b80d8
20 files changed