Revert "[LV] Don't add blocks to loop in GeneratedRTChecks (NFC)."

This reverts commit 2fd6f8f.

This missed a possible case, causing buildbot failures.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -2082,6 +2082,9 @@ class GeneratedRTChecks {
 
     auto *Pred = LoopVectorPreHeader->getSinglePredecessor();
     BranchInst::Create(LoopVectorPreHeader, SCEVCheckBlock);
+    // Create new preheader for vector loop.
+    if (OuterLoop)
+      OuterLoop->addBasicBlockToLoop(SCEVCheckBlock, *LI);
 
     SCEVCheckBlock->getTerminator()->eraseFromParent();
     SCEVCheckBlock->moveBefore(LoopVectorPreHeader);
@@ -2119,6 +2122,9 @@ class GeneratedRTChecks {
     DT->changeImmediateDominator(LoopVectorPreHeader, MemCheckBlock);
     MemCheckBlock->moveBefore(LoopVectorPreHeader);
 
+    if (OuterLoop)
+      OuterLoop->addBasicBlockToLoop(MemCheckBlock, *LI);
+
     BranchInst &BI =
         *BranchInst::Create(Bypass, LoopVectorPreHeader, MemRuntimeCheckCond);
     if (AddBranchWeights) {