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/Assembler/2010-02-05-FunctionLocalMetadataBecomesNull.ll b/llvm/test/Assembler/2010-02-05-FunctionLocalMetadataBecomesNull.ll
index 8a6735f..df9719b 100644
--- a/llvm/test/Assembler/2010-02-05-FunctionLocalMetadataBecomesNull.ll
+++ b/llvm/test/Assembler/2010-02-05-FunctionLocalMetadataBecomesNull.ll
@@ -26,7 +26,7 @@
 
 !7 = !{!1}
 !6 = !DICompileUnit(language: DW_LANG_C99, producer: "clang version 3.0 (trunk 131941)", isOptimized: true, emissionKind: 0, file: !8, enums: !9, retainedTypes: !9, subprograms: !7)
-!0 = !DILocalVariable(tag: DW_TAG_auto_variable, name: "c", line: 2, scope: !1, file: !2, type: !5)
+!0 = !DILocalVariable(name: "c", line: 2, scope: !1, file: !2, type: !5)
 !1 = !DISubprogram(name: "main", line: 1, isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: false, scopeLine: 1, file: !8, scope: !2, type: !3, function: i32 ()* @main)
 !2 = !DIFile(filename: "/d/j/debug-test.c", directory: "/Volumes/Data/b")
 !3 = !DISubroutineType(types: !4)