[dwarfdump] Add pretty printer for accelerator table based on Atom.

For instance, When dumping .apple_types, the second atom represents the
DW_TAG. In addition to printing the raw value, we now also pretty print
the value if the ATOM tells us how.

llvm-svn: 337026
diff --git a/llvm/lib/BinaryFormat/Dwarf.cpp b/llvm/lib/BinaryFormat/Dwarf.cpp
index a2e86c7..5984de7 100644
--- a/llvm/lib/BinaryFormat/Dwarf.cpp
+++ b/llvm/lib/BinaryFormat/Dwarf.cpp
@@ -571,6 +571,17 @@
   return StringRef();
 }
 
+StringRef llvm::dwarf::AtomValueString(uint16_t Atom, unsigned Val) {
+  switch (Atom) {
+  case DW_ATOM_null:
+    return "NULL";
+  case DW_ATOM_die_tag:
+    return TagString(Val);
+  }
+
+  return StringRef();
+}
+
 StringRef llvm::dwarf::IndexString(unsigned Idx) {
   switch (Idx) {
   default: