Use Hostx64/arm crossgen by default on Linux
Use Hostx64/arm crossgen by default on Linux

poizan42/coreclr,cshung/coreclr,wtgodbe/coreclr,cshung/coreclr,poizan42/coreclr,wtgodbe/coreclr,mmitche/coreclr,poizan42/coreclr,poizan42/coreclr,wtgodbe/coreclr,cshung/coreclr,poizan42/coreclr,krk/coreclr,cshung/coreclr,mmitche/coreclr,mmitche/coreclr,krk/coreclr,mmitche/coreclr,mmitche/coreclr,poizan42/coreclr,wtgodbe/coreclr,krk/coreclr,cshung/coreclr,wtgodbe/coreclr,krk/coreclr,cshung/coreclr,wtgodbe/coreclr,mmitche/coreclr,krk/coreclr,krk/coreclr