Shouldn't I add flag to winnt.h in a separate patch? The change I made to FixupVTable is for avoiding calling times assembly_from_hmodule twice when called from _CorDllMain (which involves extra heap allocation/free). If you think it is not an issue I can simplify the patch and do not touch FixupVTable. Or change FixupVTable as first part, then the main change as the next part.
Ah, that makes sense now. I missed what you were doing with FixupVTable. I don't think parsing the header multiple times is a problem, but it also makes sense this way.
I think I've seen header changes done both ways.