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/missing-file-line.ll b/llvm/test/DebugInfo/X86/missing-file-line.ll
index 455868c..d98a0a8 100644
--- a/llvm/test/DebugInfo/X86/missing-file-line.ll
+++ b/llvm/test/DebugInfo/X86/missing-file-line.ll
@@ -46,7 +46,7 @@
 !7 = !{i32 2, !"Dwarf Version", i32 4}
 !8 = !{i32 2, !"Debug Info Version", i32 3}
 !9 = !{!"clang"}
-!10 = !DILocalVariable(tag: DW_TAG_auto_variable, name: "x", scope: !4, file: !1, line: 8, type: !11)
+!10 = !DILocalVariable(name: "x", scope: !4, file: !1, line: 8, type: !11)
 !11 = !DIDerivedType(tag: DW_TAG_typedef, name: "SS", baseType: !12)
 !12 = !DICompositeType(tag: DW_TAG_structure_type, name: "S", size: 64, align: 64, elements: !13)
 !13 = !{!14}