Automerge: [VPlan] Bail out before construction VPlan0 if MinVF > MaxVF.

This reduces the cases where we need to create initial VPlans
unnecessarily after 567b317.

buildVPlansWithVPRecipes is called with MinVF > MaxVF if the target does
not support scalable vectors.

Recovers some of the compile-time impact
http://llvm-compile-time-tracker.com/compare.php?from=3033f202f6707937cd28c2473479db134993f96f&to=1a0b9e5834f7fd4abf058864e656f8e26b7a26ff&stat=instructions:u

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -8708,6 +8708,9 @@ VPRecipeBuilder::tryToCreatePartialReduction(Instruction *Reduction,
 
 void LoopVectorizationPlanner::buildVPlansWithVPRecipes(ElementCount MinVF,
                                                         ElementCount MaxVF) {
+  if (ElementCount::isKnownGT(MinVF, MaxVF))
+    return;
+
   assert(OrigLoop->isInnermost() && "Inner loop expected.");
 
   const LoopAccessInfo *LAI = Legal->getLAI();