[ORC] Add SerializationTraits for std::set and std::map.

Also, make SerializationTraits for pairs forward the actual pair
template type arguments to the underlying serializer. This allows, for example,
std::pair<StringRef, bool> to be passed as an argument to an RPC call expecting
a std::pair<std::string, bool>, since there is an underlying serializer from
StringRef to std::string that can be used.

llvm-svn: 338305