Extend usage of C++11 direct init in __debug::vector

[François Dumont]

This patch extend usage of C++11 direct initialization in 
__debug::vector and makes some calls to operator - more consistent.

Note that I also rewrote following expression in erase method:
-      return begin() + (__first.base() - cbegin().base());
+      return { _Base::begin() + (__first.base() - _Base::cbegin()), this };

The latter version was building 2 safe iterators and incrementing 1 with 
the additional debug check inherent to such an operation whereas the new 
version just build 1 safe iterator with directly the expected offset.

2018-10-15  François Dumont  <fdum...@gcc.gnu.org>

    * include/debug/vector (vector<>::cbegin()): Use C++11 direct
    initialization.
    (vector<>::cend()): Likewise.
    (vector<>::emplace(const_iterator, _Args&&...)): Likewise and use
    consistent iterator comparison.
    (vector<>::insert(const_iterator, size_type, const _Tp&)): Likewise.
    (vector<>::insert(const_iterator, _InputIterator, _InputIterator)):
    Likewise.
    (vector<>::erase(const_iterator)): Likewise.
    (vector<>::erase(const_iterator, const_iterator)): Likewise.

Tested under Linux x86_64 Debug mode and committed.

François

diff --git a/libstdc++-v3/include/debug/vector b/libstdc++-v3/include/debug/vector
index ff9f5f47c24..c11ddbb7048 100644
--- a/libstdc++-v3/include/debug/vector
+++ b/libstdc++-v3/include/debug/vector
@@ -328,11 +328,11 @@ namespace __debug
 #if __cplusplus >= 201103L
       const_iterator
       cbegin() const noexcept
-      { return const_iterator(_Base::begin(), this); }
+      { return { _Base::begin(), this }; }
 
       const_iterator
       cend() const noexcept
-      { return const_iterator(_Base::end(), this); }
+      { return { _Base::end(), this }; }
 
       const_reverse_iterator
       crbegin() const noexcept
@@ -521,7 +521,7 @@ namespace __debug
 	{
 	  __glibcxx_check_insert(__position);
 	  bool __realloc = this->_M_requires_reallocation(this->size() + 1);
-	  difference_type __offset = __position.base() - _Base::begin();
+	  difference_type __offset = __position.base() - _Base::cbegin();
 	  _Base_iterator __res = _Base::emplace(__position.base(),
 						std::forward<_Args>(__args)...);
 	  if (__realloc)
@@ -529,7 +529,7 @@ namespace __debug
 	  else
 	    this->_M_invalidate_after_nth(__offset);
 	  this->_M_update_guaranteed_capacity();
-	  return iterator(__res, this);
+	  return { __res, this };
 	}
 #endif
 
@@ -542,7 +542,8 @@ namespace __debug
       {
 	__glibcxx_check_insert(__position);
 	bool __realloc = this->_M_requires_reallocation(this->size() + 1);
-	difference_type __offset = __position.base() - _Base::begin();
+	difference_type __offset
+	  = __position.base() - __position._M_get_sequence()->_M_base().begin();
 	_Base_iterator __res = _Base::insert(__position.base(), __x);
 	if (__realloc)
 	  this->_M_invalidate_all();
@@ -577,7 +578,7 @@ namespace __debug
 	else
 	  this->_M_invalidate_after_nth(__offset);
 	this->_M_update_guaranteed_capacity();
-	return iterator(__res, this);
+	return { __res, this };
       }
 #else
       void
@@ -623,7 +624,7 @@ namespace __debug
 	  else
 	    this->_M_invalidate_after_nth(__offset);
 	  this->_M_update_guaranteed_capacity();
-	  return iterator(__res, this);
+	  return { __res, this };
 	}
 #else
       template<class _InputIterator>
@@ -661,7 +662,8 @@ namespace __debug
 #endif
       {
 	__glibcxx_check_erase(__position);
-	difference_type __offset = __position.base() - _Base::begin();
+	difference_type __offset
+	  = __position.base() - __position._M_get_sequence()->_M_base().begin();
 	_Base_iterator __res = _Base::erase(__position.base());
 	this->_M_invalidate_after_nth(__offset);
 	return iterator(__res, this);
@@ -680,7 +682,8 @@ namespace __debug
 
 	if (__first.base() != __last.base())
 	  {
-	    difference_type __offset = __first.base() - _Base::begin();
+	    difference_type __offset =
+	      __first.base() - __first._M_get_sequence()->_M_base().begin();
 	    _Base_iterator __res = _Base::erase(__first.base(),
 						__last.base());
 	    this->_M_invalidate_after_nth(__offset);
@@ -688,7 +691,7 @@ namespace __debug
 	  }
 	else
 #if __cplusplus >= 201103L
-	  return begin() + (__first.base() - cbegin().base());
+	  return { _Base::begin() + (__first.base() - _Base::cbegin()), this };
 #else
 	  return __first;
 #endif