[Utils] Use llvm::partition (NFC) (llvm#137494)

Author: kazutakahirata

llvm/lib/Transforms/Utils/FixIrreducible.cpp

@@ -135,10 +135,9 @@ static void reconnectChildLoops(LoopInfo &LI, Loop *ParentLoop, Loop *NewLoop,
                                     : LI.getTopLevelLoopsVector();
   // Any candidate is a child iff its header is owned by the new loop. Move all
   // the children to a new vector.
-  auto FirstChild = std::partition(
-      CandidateLoops.begin(), CandidateLoops.end(), [&](Loop *L) {
-        return NewLoop == L || !NewLoop->contains(L->getHeader());
-      });
+  auto FirstChild = llvm::partition(CandidateLoops, [&](Loop *L) {
+    return NewLoop == L || !NewLoop->contains(L->getHeader());
+  });
   SmallVector<Loop *, 8> ChildLoops(FirstChild, CandidateLoops.end());
   CandidateLoops.erase(FirstChild, CandidateLoops.end());