When resolving constants on a dynamically declared class during
preloading, the enum class may not be available. Fail gracefully
in that case.
Possibly we shouldn't be trying to evaluate constants on
non-linked classes at all?
We need to discard objects in the class constants if they happened
to be evaluated during preloading. To allow doing so, we need to
use mutable_data, which will place the evaluated constants into
a separate table.
