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/ARM/single-constant-use-preserves-dbgloc.ll b/llvm/test/DebugInfo/ARM/single-constant-use-preserves-dbgloc.ll
index 396eb4f..fc92dd8 100644
--- a/llvm/test/DebugInfo/ARM/single-constant-use-preserves-dbgloc.ll
+++ b/llvm/test/DebugInfo/ARM/single-constant-use-preserves-dbgloc.ll
@@ -58,7 +58,7 @@
 !7 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
 !8 = !{i32 2, !"Dwarf Version", i32 4}
 !9 = !{i32 2, !"Debug Info Version", i32 3}
-!10 = !DILocalVariable(tag: DW_TAG_auto_variable, name: "x", scope: !4, file: !1, line: 3, type: !7)
+!10 = !DILocalVariable(name: "x", scope: !4, file: !1, line: 3, type: !7)
 !11 = !DIExpression()
 !12 = !DILocation(line: 3, column: 9, scope: !4)
 !13 = !DILocation(line: 4, column: 9, scope: !14)