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/Assembler/2010-02-05-FunctionLocalMetadataBecomesNull.ll b/llvm/test/Assembler/2010-02-05-FunctionLocalMetadataBecomesNull.ll
index 5cb869d..f387a0f 100644
--- a/llvm/test/Assembler/2010-02-05-FunctionLocalMetadataBecomesNull.ll
+++ b/llvm/test/Assembler/2010-02-05-FunctionLocalMetadataBecomesNull.ll
@@ -12,7 +12,7 @@
 
 define i32 @main() nounwind readonly {
   %diff1 = alloca i64                             ; <i64*> [#uses=2]
-  call void @llvm.dbg.declare(metadata !{i64* %diff1}, metadata !0, metadata !{metadata !"0x102"})
+  call void @llvm.dbg.declare(metadata i64* %diff1, metadata !0, metadata !{!"0x102"})
   store i64 72, i64* %diff1, align 8
   %v1 = load %struct.test** @TestArrayPtr, align 8 ; <%struct.test*> [#uses=1]
   %v2 = ptrtoint %struct.test* %v1 to i64 ; <i64> [#uses=1]
@@ -23,13 +23,13 @@
 
 declare void @llvm.dbg.declare(metadata, metadata, metadata) nounwind readnone
 
-!7 = metadata !{metadata !1}
-!6 = metadata !{metadata !"0x11\0012\00clang version 3.0 (trunk 131941)\001\00\000\00\000", metadata !8, metadata !9, metadata !9, metadata !7, null, null} ; [ DW_TAG_compile_unit ]
-!0 = metadata !{metadata !"0x100\00c\002\000", metadata !1, metadata !2, metadata !5} ; [ DW_TAG_auto_variable ]
-!1 = metadata !{metadata !"0x2e\00main\00main\00\001\000\001\000\006\00256\000\001", metadata !8, metadata !2, metadata !3, null, i32 ()* @main, null, null, null} ; [ DW_TAG_subprogram ]
-!2 = metadata !{metadata !"0x29", metadata !8} ; [ DW_TAG_file_type ]
-!3 = metadata !{metadata !"0x15\00\000\000\000\000\000\000", metadata !8, metadata !2, null, metadata !4, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
-!4 = metadata !{metadata !5}
-!5 = metadata !{metadata !"0x24\00int\000\0032\0032\000\000\005", null, metadata !6} ; [ DW_TAG_base_type ]
-!8 = metadata !{metadata !"/d/j/debug-test.c", metadata !"/Volumes/Data/b"}
-!9 = metadata !{i32 0}
+!7 = !{!1}
+!6 = !{!"0x11\0012\00clang version 3.0 (trunk 131941)\001\00\000\00\000", !8, !9, !9, !7, null, null} ; [ DW_TAG_compile_unit ]
+!0 = !{!"0x100\00c\002\000", !1, !2, !5} ; [ DW_TAG_auto_variable ]
+!1 = !{!"0x2e\00main\00main\00\001\000\001\000\006\00256\000\001", !8, !2, !3, null, i32 ()* @main, null, null, null} ; [ DW_TAG_subprogram ]
+!2 = !{!"0x29", !8} ; [ DW_TAG_file_type ]
+!3 = !{!"0x15\00\000\000\000\000\000\000", !8, !2, null, !4, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!4 = !{!5}
+!5 = !{!"0x24\00int\000\0032\0032\000\000\005", null, !6} ; [ DW_TAG_base_type ]
+!8 = !{!"/d/j/debug-test.c", !"/Volumes/Data/b"}
+!9 = !{i32 0}