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/PowerPC/tls.ll b/llvm/test/DebugInfo/PowerPC/tls.ll
index 22da193..be63136 100644
--- a/llvm/test/DebugInfo/PowerPC/tls.ll
+++ b/llvm/test/DebugInfo/PowerPC/tls.ll
@@ -17,13 +17,13 @@
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!7, !8}
 
-!0 = metadata !{metadata !"0x11\004\00clang version 3.4 \000\00\000\00\000", metadata !1, metadata !2, metadata !2, metadata !2, metadata !3, metadata !2} ; [ DW_TAG_compile_unit ] [/tmp/tls.cpp] [DW_LANG_C_plus_plus]
-!1 = metadata !{metadata !"tls.cpp", metadata !"/tmp"}
-!2 = metadata !{}
-!3 = metadata !{metadata !4}
-!4 = metadata !{metadata !"0x34\00tls\00tls\00\001\000\001", null, metadata !5, metadata !6, i32* @tls, null} ; [ DW_TAG_variable ] [tls] [line 1] [def]
-!5 = metadata !{metadata !"0x29", metadata !1}          ; [ DW_TAG_file_type ] [/tmp/tls.cpp]
-!6 = 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]
-!7 = metadata !{i32 2, metadata !"Dwarf Version", i32 3}
+!0 = !{!"0x11\004\00clang version 3.4 \000\00\000\00\000", !1, !2, !2, !2, !3, !2} ; [ DW_TAG_compile_unit ] [/tmp/tls.cpp] [DW_LANG_C_plus_plus]
+!1 = !{!"tls.cpp", !"/tmp"}
+!2 = !{}
+!3 = !{!4}
+!4 = !{!"0x34\00tls\00tls\00\001\000\001", null, !5, !6, i32* @tls, null} ; [ DW_TAG_variable ] [tls] [line 1] [def]
+!5 = !{!"0x29", !1}          ; [ DW_TAG_file_type ] [/tmp/tls.cpp]
+!6 = !{!"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]
+!7 = !{i32 2, !"Dwarf Version", i32 3}
 
-!8 = metadata !{i32 1, metadata !"Debug Info Version", i32 2}
+!8 = !{i32 1, !"Debug Info Version", i32 2}