[PowerPC] Change std::sort to llvm::sort in response to r327219

Summary:
r327219 added wrappers to std::sort which randomly shuffle the container before sorting.
This will help in uncovering non-determinism caused due to undefined sorting
order of objects having the same key.

To make use of that infrastructure we need to invoke llvm::sort instead of std::sort.

Note: This patch is one of a series of patches to replace *all* std::sort to llvm::sort.
Refer the comments section in D44363 for a list of all the required patches.

Reviewers: hfinkel, RKSimon

Reviewed By: RKSimon

Subscribers: nemanjai, kbarton, llvm-commits

Differential Revision: https://reviews.llvm.org/D44870

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@329535 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/PowerPC/PPCISelDAGToDAG.cpp

@@ -1394,7 +1394,7 @@ class BitPermutationSelector {
     for (auto &I : ValueRots) {
       ValueRotsVec.push_back(I.second);
     }
-    std::sort(ValueRotsVec.begin(), ValueRotsVec.end());
+    llvm::sort(ValueRotsVec.begin(), ValueRotsVec.end());
   }
 
   // In 64-bit mode, rlwinm and friends have a rotation operator that