[JumpThreading] Dont RAUW condition incorrectly

Summary:
We have a bug when RAUWing the condition if experimental.guard or assumes is a use of that
condition. This is because LazyValueInfo may have used the guards/assumes to identify the
value of the condition at the end of the block. RAUW replaces the uses
at the guard/assume as well as uses before the guard/assume. Both of
these are incorrect.
For now, disable RAUW for conditions and fix the logic as a next
step: https://reviews.llvm.org/D33257

Reviewers: sanjoy, reames, trentxintong

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D33279

llvm-svn: 303349