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/CodeGen/Generic/dbg_value.ll b/llvm/test/CodeGen/Generic/dbg_value.ll
index 9fe4bf3..ba0a678 100644
--- a/llvm/test/CodeGen/Generic/dbg_value.ll
+++ b/llvm/test/CodeGen/Generic/dbg_value.ll
@@ -11,4 +11,4 @@
 declare void @llvm.dbg.value(metadata, i64, metadata, metadata) nounwind readnone
 
 ; !0 should conform to the format of DIVariable.
-!0 = !DILocalVariable(tag: DW_TAG_arg_variable, name: "a", arg: 1, scope: !DISubprogram())
+!0 = !DILocalVariable(name: "a", arg: 1, scope: !DISubprogram())