[VPlan] Remove recipes from back to front.

Update the deletion order when destroying VPBasicBlocks. This ensures
recipes that depend on earlier ones in the block are removed first.
Otherwise this may cause issues when recipes have remaining users later
in the block.

lib/Transforms/Vectorize/VPlan.h

@@ -1309,7 +1309,10 @@ public:
       appendRecipe(Recipe);
   }
 
-  ~VPBasicBlock() override { Recipes.clear(); }
+  ~VPBasicBlock() override {
+    while (!Recipes.empty())
+      Recipes.pop_back();
+  }
 
   /// Instruction iterators...
   using iterator = RecipeListTy::iterator;