Emit trailing padding on constant vectors when TargetData says that the vector

Emit trailing padding on constant vectors when TargetData says that the vector
is larger than the sum of the elements (including per-element padding).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@133631 91177308-0d34-0410-b5e6-96231b3b80d8