We should raise an exception rather than crash when reference and valuetype fields overlap. However, detecting this in mono has proven more difficult than expected. I am resolving this for now as this crash only occurs in a low likelihood event, where a user has explicitly overlapped reference and valuetype fields via Explicit layout.

// Avoid code like the following

[StructLayout(LayoutKind.Explicit)]
public struct GCCrasher
{
[FieldOffset(0)] public int valueType;
[FieldOffset(0)] public GameObject referenceType;
}