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

test/Transforms/IPConstantProp/user-with-multiple-uses.ll

@@ -4,7 +4,7 @@
 ; IPSCCP should propagate the 0 argument, eliminate the switch, and propagate
 ; the result.
 
-; CHECK: define i32 @main() noreturn nounwind {
+; CHECK: define i32 @main() #0 {
 ; CHECK-NEXT: entry:
 ; CHECK-NEXT: %call2 = tail call i32 @wwrite(i64 0) nounwind
 ; CHECK-NEXT: ret i32 123
@@ -28,3 +28,6 @@ sw.default:
 return:
   ret i32 0
 }
+
+; CHECK: attributes #0 = { noreturn nounwind }
+; CHECK: attributes #1 = { nounwind readnone }