IR: Make metadata typeless in assembly

Now that `Metadata` is typeless, reflect that in the assembly.  These
are the matching assembly changes for the metadata/value split in
r223802.

  - Only use the `metadata` type when referencing metadata from a call
    intrinsic -- i.e., only when it's used as a `Value`.

  - Stop pretending that `ValueAsMetadata` is wrapped in an `MDNode`
    when referencing it from call intrinsics.

So, assembly like this:

    define @foo(i32 %v) {
      call void @llvm.foo(metadata !{i32 %v}, metadata !0)
      call void @llvm.foo(metadata !{i32 7}, metadata !0)
      call void @llvm.foo(metadata !1, metadata !0)
      call void @llvm.foo(metadata !3, metadata !0)
      call void @llvm.foo(metadata !{metadata !3}, metadata !0)
      ret void, !bar !2
    }
    !0 = metadata !{metadata !2}
    !1 = metadata !{i32* @global}
    !2 = metadata !{metadata !3}
    !3 = metadata !{}

turns into this:

    define @foo(i32 %v) {
      call void @llvm.foo(metadata i32 %v, metadata !0)
      call void @llvm.foo(metadata i32 7, metadata !0)
      call void @llvm.foo(metadata i32* @global, metadata !0)
      call void @llvm.foo(metadata !3, metadata !0)
      call void @llvm.foo(metadata !{!3}, metadata !0)
      ret void, !bar !2
    }
    !0 = !{!2}
    !1 = !{i32* @global}
    !2 = !{!3}
    !3 = !{}

I wrote an upgrade script that handled almost all of the tests in llvm
and many of the tests in cfe (even handling many `CHECK` lines).  I've
attached it (or will attach it in a moment if you're speedy) to PR21532
to help everyone update their out-of-tree testcases.

This is part of PR21532.

llvm-svn: 224257
diff --git a/llvm/test/DebugInfo/X86/dwarf-aranges.ll b/llvm/test/DebugInfo/X86/dwarf-aranges.ll
index 237e418..28fb9e5 100644
--- a/llvm/test/DebugInfo/X86/dwarf-aranges.ll
+++ b/llvm/test/DebugInfo/X86/dwarf-aranges.ll
@@ -62,20 +62,20 @@
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!13, !16}
 
-!0 = metadata !{metadata !"0x11\0012\00clang version 3.4 \000\00\000\00\000", metadata !1, metadata !2, metadata !2, metadata !3, metadata !8, metadata !2} ; [ DW_TAG_compile_unit ] [/home/kayamon/test.c] [DW_LANG_C99]
-!1 = metadata !{metadata !"test.c", metadata !"/home/kayamon"}
-!2 = metadata !{}
-!3 = metadata !{metadata !4}
-!4 = metadata !{metadata !"0x2e\00some_code\00some_code\00\005\000\001\000\006\000\000\006", metadata !1, metadata !5, metadata !6, null, void ()* @some_code, null, null, metadata !2} ; [ DW_TAG_subprogram ] [line 5] [def] [scope 6] [some_code]
-!5 = metadata !{metadata !"0x29", metadata !1}          ; [ DW_TAG_file_type ] [/home/kayamon/test.c]
-!6 = metadata !{metadata !"0x15\00\000\000\000\000\000\000", i32 0, null, null, metadata !7, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
-!7 = metadata !{null}
-!8 = metadata !{metadata !9, metadata !11, metadata !12}
-!9 = metadata !{metadata !"0x34\00some_data\00some_data\00\001\000\001", null, metadata !5, metadata !10, i32* @some_data, null} ; [ DW_TAG_variable ] [some_data] [line 1] [def]
-!10 = metadata !{metadata !"0x24\00int\000\0032\0032\000\000\005", null, null} ; [ DW_TAG_base_type ] [int] [line 0, size 32, align 32, offset 0, enc DW_ATE_signed]
-!11 = metadata !{metadata !"0x34\00some_other\00some_other\00\003\000\001", null, metadata !5, metadata !10, i32* @some_other, null} ; [ DW_TAG_variable ] [some_other] [line 3] [def]
-!12 = metadata !{metadata !"0x34\00some_bss\00some_bss\00\002\000\001", null, metadata !5, metadata !10, i32* @some_bss, null} ; [ DW_TAG_variable ] [some_bss] [line 2] [def]
-!13 = metadata !{i32 2, metadata !"Dwarf Version", i32 4}
-!14 = metadata !{i32 7, i32 0, metadata !4, null}
-!15 = metadata !{i32 8, i32 0, metadata !4, null}
-!16 = metadata !{i32 1, metadata !"Debug Info Version", i32 2}
+!0 = !{!"0x11\0012\00clang version 3.4 \000\00\000\00\000", !1, !2, !2, !3, !8, !2} ; [ DW_TAG_compile_unit ] [/home/kayamon/test.c] [DW_LANG_C99]
+!1 = !{!"test.c", !"/home/kayamon"}
+!2 = !{}
+!3 = !{!4}
+!4 = !{!"0x2e\00some_code\00some_code\00\005\000\001\000\006\000\000\006", !1, !5, !6, null, void ()* @some_code, null, null, !2} ; [ DW_TAG_subprogram ] [line 5] [def] [scope 6] [some_code]
+!5 = !{!"0x29", !1}          ; [ DW_TAG_file_type ] [/home/kayamon/test.c]
+!6 = !{!"0x15\00\000\000\000\000\000\000", i32 0, null, null, !7, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!7 = !{null}
+!8 = !{!9, !11, !12}
+!9 = !{!"0x34\00some_data\00some_data\00\001\000\001", null, !5, !10, i32* @some_data, null} ; [ DW_TAG_variable ] [some_data] [line 1] [def]
+!10 = !{!"0x24\00int\000\0032\0032\000\000\005", null, null} ; [ DW_TAG_base_type ] [int] [line 0, size 32, align 32, offset 0, enc DW_ATE_signed]
+!11 = !{!"0x34\00some_other\00some_other\00\003\000\001", null, !5, !10, i32* @some_other, null} ; [ DW_TAG_variable ] [some_other] [line 3] [def]
+!12 = !{!"0x34\00some_bss\00some_bss\00\002\000\001", null, !5, !10, i32* @some_bss, null} ; [ DW_TAG_variable ] [some_bss] [line 2] [def]
+!13 = !{i32 2, !"Dwarf Version", i32 4}
+!14 = !{i32 7, i32 0, !4, null}
+!15 = !{i32 8, i32 0, !4, null}
+!16 = !{i32 1, !"Debug Info Version", i32 2}