* sem_disp.adb (Check_Dispatching_Operation): if the dispatching
operation is a body without previous spec, update the list of
primitive operations to ensure that cross-reference information is
up-to-date.
* sem_ch12.adb (Build_Instance_Compilation_Unit_Nodes): When creating a
new compilation unit node for the instance declaration, keep the
context items of the original unit on it, so that the context of the
instance body only holds the context inherited from the generic body.