Add enums and some cleanup (#148)

* support enums

* better compiler warnings

* tweaks to build with clang

decompiler/IR/IR.h

@@ -27,6 +27,7 @@ class IR {
   virtual TP_Type get_expression_type(const TypeState& input,
                                       const LinkedObjectFile& file,
                                       DecompilerTypeSystem& dts);
+  virtual ~IR() = default;
 };
 
 class IR_Atomic : public virtual IR {

decompiler/data/tpage.h

@@ -1,6 +1,6 @@
 #pragma once
 
-class ObjectFileData;
+struct ObjectFileData;
 
 struct TPageResultStats {
   int total_textures = 0;