Fix C++11-ism in C++98 member function

	* include/debug/string (insert(__const_iterator, _InIter, _InIter)):
	[!_GLIBCXX_USE_CXX11_ABI]: Replace use of C++11-only cbegin() with
	begin(), for C++98 compatibility.

From-SVN: r263809

libstdc++-v3/ChangeLog

 2018-08-23  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/debug/string (insert(__const_iterator, _InIter, _InIter)):
+	[!_GLIBCXX_USE_CXX11_ABI]: Replace use of C++11-only cbegin() with
+	begin(), for C++98 compatibility.
+
 	* include/bits/basic_string.h [_GLIBCXX_USE_CXX11_ABI]
 	(basic_string::__const_iterator): Change access to protected.
 	[!_GLIBCXX_USE_CXX11_ABI] (basic_string::__const_iterator): Define

libstdc++-v3/include/debug/string

@@ -642,7 +642,7 @@ namespace __gnu_debug
 	  else
 	    __res = _Base::insert(__p.base(), __first, __last);
 #else
-	  const size_type __offset = __p.base() - _Base::cbegin();
+	  const size_type __offset = __p.base() - _Base::begin();
 	  _Base::insert(__p.base(), __first, __last);
 	  __res = _Base::begin() + __offset;
 #endif