For -Wconsumed, walk the namespaces to find if the top most namespace is "std"

For -Wconsumed, walk the namespaces to find if the top most namespace is "std"
to determine if a move function is the std::move function.  This allows functions
like std::__1::move to also be treated a the move function.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@197445 91177308-0d34-0410-b5e6-96231b3b80d8