Replace safe bool idiom with explicit operator bool

	* include/ext/pointer.h [__cplusplus >= 201103L]
	(_Pointer_adapter::operator bool): Add explicit conversion operator
	to replace safe bool idiom.

From-SVN: r263162

libstdc++-v3/ChangeLog

+2018-07-31  Jonathan Wakely  <jwakely@redhat.com>
+
+	* include/ext/pointer.h [__cplusplus >= 201103L]
+	(_Pointer_adapter::operator bool): Add explicit conversion operator
+	to replace safe bool idiom.
+
 2018-07-30  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/86734

libstdc++-v3/include/ext/pointer.h

@@ -356,6 +356,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       { return _Storage_policy::get()[__index]; }
 
       // To allow implicit conversion to "bool", for "if (ptr)..."
+#if __cplusplus >= 201103L
+      explicit operator bool() const { return _Storage_policy::get() != 0; }
+#else
     private:
       typedef element_type*(_Pointer_adapter::*__unspecified_bool_type)() const;
 
@@ -370,6 +373,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       inline bool
       operator!() const 
       { return (_Storage_policy::get() == 0); }
+#endif
   
       // Pointer differences
       inline friend std::ptrdiff_t