[DFAJumpThreading] make update order deterministic

We tracked down some non-determinism in compilation output to the
DFAJumpThreading pass. These changes fixed our issue:

* Make the DefMap type a MapVector to make its iteration order depend on
  insertion order.
* Sort the values to be inserted into NewDefs by instruction order to
  make the insertion order deterministic. Since these values come from
  iterating over a ValueMap, which doesn't have deterministic iteration
  order, I couldn't fix this at its source.

Reviewed By: alexey.zhikhar

Differential Revision: https://reviews.llvm.org/D118590