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/restrict.ll b/llvm/test/DebugInfo/restrict.ll
index 71d94f6..330d31a 100644
--- a/llvm/test/DebugInfo/restrict.ll
+++ b/llvm/test/DebugInfo/restrict.ll
@@ -48,6 +48,6 @@
 !10 = !{i32 2, !"Dwarf Version", i32 4}
 !11 = !{i32 1, !"Debug Info Version", i32 3}
 !12 = !{!"clang version 3.5.0 "}
-!13 = !DILocalVariable(tag: DW_TAG_arg_variable, name: "dst", line: 1, arg: 1, scope: !4, file: !5, type: !8)
+!13 = !DILocalVariable(name: "dst", line: 1, arg: 1, scope: !4, file: !5, type: !8)
 !14 = !DILocation(line: 1, scope: !4)
 !15 = !DILocation(line: 2, scope: !4)