The base VMCache class changed to the generic_ types with their
introduction in in *2011* (435c43f5912b109e7d5cf682865d2061e62fad8c),
but these classes were never properly adapted. These functions should not
be called here (they panic() -- but the base class only returns B_ERROR,
so that is a difference at least.)
Found by Clang's -Woverloaded-virtual.
bf77c15232