Disasmo overrides project's DefineConstants

[saucecontrol]

Since the dotnet build cmdline now includes /p:DefineConstants=DISASMO, this value is taken instead of any value defined in the csproj.

I like being able to detect Disasmo runs from my project and/or code, but maybe an alternate property would be better. We could then bridge that into DefineConstants ourselves if we want that.

[teo-tsirpanis]

Fixed by 2649e96.