[OPENMP] Fix for PR34398: assert with random access iterator if the

step>1.

If the loop is a loot with random access iterators and the iteration
construct is represented it += n, then the compiler crashed because of
reusing of the same MaterializedTemporaryExpr around N. Patch fixes it
by using the expression as written, without any special kind of
wrappings.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@312292 91177308-0d34-0410-b5e6-96231b3b80d8