Improve use of CfgLocalAllocator and introduce containers that use it.

src/IceInst.h

Index: src/IceInst.h
diff --git a/src/IceInst.h b/src/IceInst.h
index a727683011523fe5956711160d962f4bc362658a..fcd7269e9e4a4c074607a40e2c9ee170359d3120 100644
--- a/src/IceInst.h
+++ b/src/IceInst.h
@@ -161,10 +161,7 @@ public:
   void dumpDest(const Cfg *Func) const;
   virtual bool isRedundantAssign() const { return false; }
 
-  // TODO(jpp): Insts should not have non-trivial destructors, but they
-  // currently do. This dtor is marked final as a multi-step refactor that
-  // will eventually fix this problem.
-  virtual ~Inst() = default;
+  ~Inst() = default;
 
 protected:
   Inst(Cfg *Func, InstKind Kind, SizeT MaxSrcs, Variable *Dest);