private_typeinfo: limit is_dst_type_derived_from_static_type optimization

Patch by Ryan Prichard

If the destination type does not derive from the static type, we can skip
the search_above_dst call, but we still need to run the
!does_dst_type_point_to_our_static_type block of code. That block of code
will increment info->number_to_dst_ptr to 2, and because dest isn't derived
from static, the cast will ultimately fail.

Fixes PR33439

Reviewed as https://reviews.llvm.org/D36447

llvm-svn: 332767