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/arguments.ll b/llvm/test/DebugInfo/X86/arguments.ll
index 0af119b..6a58718 100644
--- a/llvm/test/DebugInfo/X86/arguments.ll
+++ b/llvm/test/DebugInfo/X86/arguments.ll
@@ -67,9 +67,9 @@
 !15 = !DIDerivedType(tag: DW_TAG_pointer_type, size: 64, align: 64, flags: DIFlagArtificial | DIFlagObjectPointer, baseType: !8)
 !16 = !DIDerivedType(tag: DW_TAG_reference_type, baseType: !17)
 !17 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !8)
-!19 = !DILocalVariable(tag: DW_TAG_arg_variable, name: "f", line: 6, arg: 1, scope: !4, file: !5, type: !8)
+!19 = !DILocalVariable(name: "f", line: 6, arg: 1, scope: !4, file: !5, type: !8)
 !20 = !DILocation(line: 6, scope: !4)
-!21 = !DILocalVariable(tag: DW_TAG_arg_variable, name: "g", line: 6, arg: 2, scope: !4, file: !5, type: !8)
+!21 = !DILocalVariable(name: "g", line: 6, arg: 2, scope: !4, file: !5, type: !8)
 !22 = !DILocation(line: 7, scope: !4)
 !23 = !DILocation(line: 8, scope: !4)
 !24 = !{i32 1, !"Debug Info Version", i32 3}