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

[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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@338305 91177308-0d34-0410-b5e6-96231b3b80d8