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/CodeGen/NVPTX/tex-read-cuda.ll b/llvm/test/CodeGen/NVPTX/tex-read-cuda.ll
index ee0cefa..c5b5600 100644
--- a/llvm/test/CodeGen/NVPTX/tex-read-cuda.ll
+++ b/llvm/test/CodeGen/NVPTX/tex-read-cuda.ll
@@ -41,6 +41,6 @@
 }
 
 !nvvm.annotations = !{!1, !2, !3}
-!1 = metadata !{void (i64, float*, i32)* @foo, metadata !"kernel", i32 1}
-!2 = metadata !{void (float*, i32)* @bar, metadata !"kernel", i32 1}
-!3 = metadata !{i64 addrspace(1)* @tex0, metadata !"texture", i32 1}
+!1 = !{void (i64, float*, i32)* @foo, !"kernel", i32 1}
+!2 = !{void (float*, i32)* @bar, !"kernel", i32 1}
+!3 = !{i64 addrspace(1)* @tex0, !"texture", i32 1}