CC: Move the _cxx attribute from rt::NativeDiosCC into Native.

divine/cc/native.hpp

@@ -95,11 +95,13 @@ namespace divine::cc
         virtual std::unique_ptr< llvm::Module > link_bitcode();
         void construct_paired_files();
         void print_info( std::string_view version );
+        void set_cxx( bool cxx ) { _cxx = cxx; }
 
         cc::ParsedOpts _po;
         PairedFiles _files;
         std::vector< std::string > _ld_args;
         cc::CC1 _clang;
+        bool _cxx;
 
         ~Native();
     };

divine/rt/dios-cc.hpp

@@ -39,9 +39,6 @@ struct NativeDiosCC : cc::Native
     auto link_dios_native( bool cxx );
     std::unique_ptr< llvm::Module > link_bitcode() override;
     void link() override;
-    void set_cxx( bool cxx ) { _cxx = cxx; }
-
-    bool _cxx;
 };
 
 } // rt