Exclude mixed-mode assemblies from being crossgenend into R2R images

[fadimounir]

Need to port check/error from desktop framework code. In CEECompileInfo::SetCompilationTarget:

#ifdef FEATURE_READYTORUN_COMPILER if (IsReadyToRunCompilation() && !pModule->GetDomainFile()->GetFile()->IsILOnly()) { GetSvcLogger()->Printf(LogLevel_Error, W("Error: Readytorun compilation is not supported for mixed mode assemblies\n")); return E_FAIL; } #endif