nsIDHashKey::HashKey(NULL);
That should be fine. The goal of the code is to trick the linker so it brings in the nsIDHashKey stuff, IIRC.
It would probably be good to file a bug on this particular issue, and if you can, attach a patch. I don't think for the purposes here you need to pass in any real value. Use nsnull not NULL, though.
Also, I know there were other issues, even after getting things to build. I believe that the Intel compiler (not sure which version), had problems with several spots in the Mozilla code. And it was a compiler issue, not a Mozilla one. Just so you're aware.
David
