WebKit and WebKitLegacy each have a copy of WebCore in them. Should at least use a SHARED WebCore when both are enabled.
Hmm, I don't like this idea because this will tend to WinCairo only build failures. WinCairo is planning to remove WebKitLegacy (Bug 194904). Do you want to this only for Bug 188175? For Bug 188175, let's take the original Steph's idea (Bug 188175 Comment 2).