Follow practices suggested by "Effective C++"

The patch adjust the code of the base, base-<kernel>, and os repository.
To adapt existing components to fix violations of the best practices
suggested by "Effective C++" as reported by the -Weffc++ compiler
argument. The changes follow the patterns outlined below:

* A class with virtual functions can no longer publicly inherit base
  classed without a vtable. The inherited object may either be moved
  to a member variable, or inherited privately. The latter would be
  used for classes that inherit 'List::Element' or 'Avl_node'. In order
  to enable the 'List' and 'Avl_tree' to access the meta data, the
  'List' must become a friend.

* Instead of adding a virtual destructor to abstract base classes,
  we inherit the new 'Interface' class, which contains a virtual
  destructor. This way, single-line abstract base classes can stay
  as compact as they are now. The 'Interface' utility resides in
  base/include/util/interface.h.

* With the new warnings enabled, all member variables must be explicitly
  initialized. Basic types may be initialized with '='. All other types
  are initialized with braces '{ ... }' or as class initializers. If
  basic types and non-basic types appear in a row, it is nice to only
  use the brace syntax (also for basic types) and align the braces.

* If a class contains pointers as members, it must now also provide a
  copy constructor and assignment operator. In the most cases, one
  would make them private, effectively disallowing the objects to be
  copied. Unfortunately, this warning cannot be fixed be inheriting
  our existing 'Noncopyable' class (the compiler fails to detect that
  the inheriting class cannot be copied and still gives the error).
  For now, we have to manually add declarations for both the copy
  constructor and assignment operator as private class members. Those
  declarations should be prepended with a comment like this:

        /*
         * Noncopyable
         */
        Thread(Thread const &);
        Thread &operator = (Thread const &);

  In the future, we should revisit these places and try to replace
  the pointers with references. In the presence of at least one
  reference member, the compiler would no longer implicitly generate
  a copy constructor. So we could remove the manual declaration.

Issue #465

repos/base-foc/src/include/base/internal/cap_alloc.h

@@ -41,8 +41,14 @@ namespace Genode {
 	{
 		private:
 
-			Spin_lock _lock; /* used very early in initialization,
-			                    where normal lock isn't feasible */
+			/*
+			 * Noncopyable
+			 */
+			Cap_index_allocator_tpl(Cap_index_allocator_tpl const &);
+			Cap_index_allocator_tpl &operator = (Cap_index_allocator_tpl const &);
+
+			Spin_lock _lock { }; /* used very early in initialization,
+			                        where normal lock isn't feasible */
 
 			enum {
 				/* everything below START_IDX is managed by core */

repos/base-foc/src/include/base/internal/cap_map.h

@@ -174,8 +174,8 @@ namespace Genode {
 	{
 		private:
 
-			Avl_tree<Cap_index> _tree;
-			Spin_lock           _lock;
+			Avl_tree<Cap_index> _tree { };
+			Spin_lock           _lock { };
 
 		public:
 

repos/base-foc/src/include/base/internal/capability_data.h

@@ -30,7 +30,8 @@ class Genode::Native_capability::Data : public Avl_node<Data>, Noncopyable
 {
 	private:
 
-		enum { INVALID_ID = -1, UNUSED = 0 };
+		constexpr static uint16_t INVALID_ID = ~0;
+		constexpr static uint16_t UNUSED     =  0;
 
 		uint8_t  _ref_cnt; /* reference counter    */
 		uint16_t _id;      /* global capability id */
@@ -47,7 +48,7 @@ class Genode::Native_capability::Data : public Avl_node<Data>, Noncopyable
 		uint8_t  dec();
 		addr_t   kcap() const;
 
-		void* operator new (__SIZE_TYPE__ size, Data* idx) { return idx; }
+		void* operator new (__SIZE_TYPE__, Data* idx) { return idx; }
 		void  operator delete (void* idx) { memset(idx, 0, sizeof(Data)); }