Use function attributes to indicate that we don't want to realign the stack.

Function attributes are the future! So just query whether we want to realign the
stack directly from the function instead of through a random target options
structure.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187618 91177308-0d34-0410-b5e6-96231b3b80d8