Add a dominanance check interface that uses caching for instructions within same basic block.

Summary:
This problem stems from the fact that instructions are allocated using new
in LLVM, i.e. there is no relationship that can be derived by just looking
at the pointer value.

This interface dispatches to appropriate dominance check given 2 instructions,
i.e. in case the instructions are in the same basic block, ordered basicblock
(with instruction numbering and caching) are used. Otherwise, dominator tree
is used.

This is a preparation patch for https://reviews.llvm.org/D32720

Reviewers: dberlin, hfinkel, davide

Subscribers: davide, mgorny, llvm-commits

Differential Revision: https://reviews.llvm.org/D33380

llvm-svn: 304764