CC: Make Native::link() virtual.

divine/cc/native.hpp

@@ -36,7 +36,7 @@ namespace divine::cc
 
         int compile_files();
         void init_ld_args();
-        void link();
+        virtual void link();
         void preprocess_only();
         int run();
         virtual std::unique_ptr< llvm::Module > link_bitcode();

divine/rt/dios-cc.hpp

@@ -38,7 +38,7 @@ struct NativeDiosCC : cc::Native
 
     auto link_dios_native( bool cxx );
     std::unique_ptr< llvm::Module > link_bitcode() override;
-    void link();
+    void link() override;
 
     bool _cxx;
 };