DebugInfo: Fix testcases that fail -verify-debug-info=true

As part of PR22777, fix testcases that fail the debug info verifier.
The changes fall into the following categories:

  - Empty `filename:` fields in `MDFile`s.  Compile units and some types
    require non-empty filenames.  A number of testcases have empty
    filenames, probably due to hand-reduction of testcases.
  - Not-quite empty arrays: `!{i32 0}`.  This used to be equivalent in
    the debug info schema to `!{}`.  They cause problems for
    `!MDSubroutineType`'s `types:` array, since it requires all operands
    to be valid types.  (Note that `!{null}` is the correct type array
    for functions that take no arguments and return `void`.)
  - Significantly bitrotted testcases.  Nodes got left behind a few
    upgrades ago because of missing or invalid tags.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232415 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/GCOVProfiling/version.ll

@@ -18,11 +18,11 @@ define void @test() {
 
 !0 = !MDCompileUnit(language: DW_LANG_C_plus_plus, producer: "clang version 3.3 (trunk 176994)", isOptimized: false, emissionKind: 0, file: !11, enums: !3, retainedTypes: !3, subprograms: !4, globals: !3)
 !2 = !MDFile(filename: "version", directory: "/usr/local/google/home/nlewycky")
-!3 = !{i32 0}
+!3 = !{}
 !4 = !{!5}
 !5 = !MDSubprogram(name: "test", line: 1, isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: false, scopeLine: 1, file: !10, scope: !6, type: !7, function: void ()* @test, variables: !3)
 !6 = !MDFile(filename: "<stdin>", directory: ".")
-!7 = !MDSubroutineType(types: !3)
+!7 = !MDSubroutineType(types: !{null})
 !8 = !MDLocation(line: 1, scope: !5)
 ;; !9 is added through the echo line at the top.
 !10 = !MDFile(filename: "<stdin>", directory: ".")