It is not implemented in gcc 4.7.2.
There is some explanation:
Just to clarify a bit: this wasn't an oversight. We had the nasty problem in the Draft C++0x Standard with std::pair, which essentially made impossible adding the emplace_* members to std::map, std::multimap, etc, without breaking existing user code. Thus we waited on that, until things got clarified in this whole area. Now it's actually possible to work on those facilities.
Your code compiles nicely with gcc 4.8.0, see LWS.