Port |Bug 918317 - [Async shutdown] Handle C++ code| to im. rs=build-system-port

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extra : amend_source : 4304f181b5ee4a0af897a8207e8c44910d12cbfb
Bug 1084973 - Port |Bug 1031352 - share the logic for determining what MSVC DLLs to package| to im, mail, and suite. r=florian,jcranmer,Callek a=Callek for a SeaMonkey CLOSED TREE