[VPlan] Process ExpressionRecipes in reverse order in constructor.
Currently there's a crash when trying to construct VPExpressionRecipes
for a mul (ext, ext), if the multiply has outside users; the mul will be
cloned to serve its external users, but the extends won't get cloned and
will stay connected to users outside the loop (the cloned multiply).
To fix this, process recipes in reverse order. This ensures that we
visit bundled users before their operands, properly ensuring that the
extends for the external user are cloned as well.
llvm-project
9c0e09e0 - [VPlan] Process ExpressionRecipes in reverse order in constructor.
