private void compare(Enum pre, Enum post) {
		if (pre.getLength() != post.getLength()) {
			Msg.error(this, "Enum data type sizes don't match: " + pre + ", " + post);
			return;
		}
	}
Object instance identity map used to prevent recursive loops when following
DataType pointers and such.  DataType path/name mapping can't be used because
there is no guarantee that impl DataType's have unique names.
<p>
Using a Map as a Set because there is no IdentityHashSet. (the value of the map entry
is not used, just the key set)
Ghidra/Features/Base/src/main/java/ghidra/app/util/bin/format/dwarf/DataTypeGraphComparator.java