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/lib/IR/DebugInfoMetadata.cpp b/llvm/lib/IR/DebugInfoMetadata.cpp
index db6da05..4adda6f 100644
--- a/llvm/lib/IR/DebugInfoMetadata.cpp
+++ b/llvm/lib/IR/DebugInfoMetadata.cpp
@@ -466,21 +466,21 @@
                        Ops);
 }
 
-DILocalVariable *DILocalVariable::getImpl(LLVMContext &Context, unsigned Tag,
-                                          Metadata *Scope, MDString *Name,
-                                          Metadata *File, unsigned Line,
-                                          Metadata *Type, unsigned Arg,
-                                          unsigned Flags, StorageType Storage,
+DILocalVariable *DILocalVariable::getImpl(LLVMContext &Context, Metadata *Scope,
+                                          MDString *Name, Metadata *File,
+                                          unsigned Line, Metadata *Type,
+                                          unsigned Arg, unsigned Flags,
+                                          StorageType Storage,
                                           bool ShouldCreate) {
   // 64K ought to be enough for any frontend.
   assert(Arg <= UINT16_MAX && "Expected argument number to fit in 16-bits");
 
   assert(Scope && "Expected scope");
   assert(isCanonical(Name) && "Expected canonical MDString");
-  DEFINE_GETIMPL_LOOKUP(DILocalVariable, (Tag, Scope, getString(Name), File,
-                                          Line, Type, Arg, Flags));
+  DEFINE_GETIMPL_LOOKUP(DILocalVariable,
+                        (Scope, getString(Name), File, Line, Type, Arg, Flags));
   Metadata *Ops[] = {Scope, Name, File, Type};
-  DEFINE_GETIMPL_STORE(DILocalVariable, (Tag, Line, Arg, Flags), Ops);
+  DEFINE_GETIMPL_STORE(DILocalVariable, (Line, Arg, Flags), Ops);
 }
 
 DIExpression *DIExpression::getImpl(LLVMContext &Context,