When checking whether a def of an aliased register is dead, ask the

When checking whether a def of an aliased register is dead, ask the
machineinstr whether the aliased register is dead, rather than the original
register is dead. This allows it to get the correct answer when examining
an instruction like this:
  CALLpcrel32 <ga:foo>, %AL<imp-def>, %EAX<imp-def,dead>
where EAX is dead but a subregister of it is still live. This fixes PR5294.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85135 91177308-0d34-0410-b5e6-96231b3b80d8