Handle ref classes with missing fields.
Handle ref classes with missing fields.

This is a more aggressive workaround for #557. We already have the ability to tolerate missing fields in codegen. So we fall back to that if we're building up a model of a ref class and can't account for all of its fields.

For value classes we still insist that we get a complete picture, because we intend to use the LLVM types to produce GC info.

russellhadley/llilc,dotnet/llilc,AndyAyersMS/llilc,JosephTremoulet/llilc,tempbottle/llilc,manu-silicon/llilc,pgavlin/llilc,tempbottle/llilc,JosephTremoulet/llilc,pgavlin/llilc,marksantos/llilc,richardlford/llilc,pgavlin/llilc,kyulee1/llilcjit,richardlford/llilc,JosephTremoulet/llilc,swaroop-sridhar/llilc,dkorolev/llilc,adiaaida/llilc,russellhadley/llilc,dotnet/llilc,richardlford/llilc,BruceForstall/llilc,kyulee1/llilcjit,russellhadley/llilc,adiaaida/llilc,BruceForstall/llilc,marksantos/llilc,AndyAyersMS/llilc,kyulee1/llilcjit,tempbottle/llilc,adiaaida/llilc,dkorolev/llilc,swaroop-sridhar/llilc,marksantos/llilc,BruceForstall/llilc,manu-silicon/llilc,swaroop-sridhar/llilc,dotnet/llilc,manu-silicon/llilc,AndyAyersMS/llilc,dkorolev/llilc