Modify the LLVM assembly output so that it uses references to represent function attributes.

This makes the LLVM assembly look better. E.g.:

     define void @foo() #0 { ret void }
     attributes #0 = { nounwind noinline ssp }


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175605 91177308-0d34-0410-b5e6-96231b3b80d8