DI: Remove DW_TAG_arg_variable and DW_TAG_auto_variable

Remove the fake `DW_TAG_auto_variable` and `DW_TAG_arg_variable` tags,
using `DW_TAG_variable` in their place Stop exposing the `tag:` field at
all in the assembly format for `DILocalVariable`.

Most of the testcase updates were generated by the following sed script:

    find test/ -name "*.ll" -o -name "*.mir" |
    xargs grep -l 'DILocalVariable' |
    xargs sed -i '' \
      -e 's/tag: DW_TAG_arg_variable, //' \
      -e 's/tag: DW_TAG_auto_variable, //'

There were only a handful of tests in `test/Assembly` that I needed to
update by hand.

(Note: a follow-up could change `DILocalVariable::DILocalVariable()` to
set the tag to `DW_TAG_formal_parameter` instead of `DW_TAG_variable`
(as appropriate), instead of having that logic magically in the backend
in `DbgVariable`.  I've added a FIXME to that effect.)

llvm-svn: 243774
diff --git a/llvm/test/DebugInfo/X86/DW_AT_location-reference.ll b/llvm/test/DebugInfo/X86/DW_AT_location-reference.ll
index 96d1e50..ae080b9 100644
--- a/llvm/test/DebugInfo/X86/DW_AT_location-reference.ll
+++ b/llvm/test/DebugInfo/X86/DW_AT_location-reference.ll
@@ -107,7 +107,7 @@
 !2 = !DICompileUnit(language: DW_LANG_C99, producer: "clang version 3.0 (trunk)", isOptimized: true, emissionKind: 1, file: !23, enums: !{}, retainedTypes: !{}, subprograms: !21, imports:  null)
 !3 = !DISubroutineType(types: !4)
 !4 = !{null}
-!5 = !DILocalVariable(tag: DW_TAG_auto_variable, name: "x", line: 5, scope: !6, file: !1, type: !7)
+!5 = !DILocalVariable(name: "x", line: 5, scope: !6, file: !1, type: !7)
 !6 = distinct !DILexicalBlock(line: 4, column: 14, file: !23, scope: !0)
 !7 = !DIBasicType(tag: DW_TAG_base_type, name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
 !8 = !DILocation(line: 6, column: 3, scope: !6)