Use the target options specified on a function to reset the back-end.

During LTO, the target options on functions within the same Module may
change. This would necessitate resetting some of the back-end. Do this for X86,
because it's a Friday afternoon.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178917 91177308-0d34-0410-b5e6-96231b3b80d8