This fixes two issues with impotc'ed types.
1. Passing an importc'ed inherited object to where superclass is
expected emitted `v.Sup` previously. Now it emits `v`, similar to cpp
codegen.
2. Casting between different nim types that resolve to the same C type
previously was done like `*(T*)&v`, now it is just `v`.
(cherry picked from commit 937e647f4f)
`hashType` proc returned the same hash value from different instanced
generics types like `D[int64]` and `D[F]`.
That caused the struct type with wrong field types.
object/tuple type size check code is generated when it is compiled with
`-d:checkAbi` option.
(cherry picked from commit 88e7adfcb7)
