[pstl] Added missing double-underscore prefixes to some types

[ismailp]

Summary

Some of the move_ types were used with leading double-underscores, but
they were declared without __ prefix.

This patch adds double-underscores to all move_ types, and their uses.

pstl/include/pstl/internal/parallel_backend_tbb.h

class __merge_task : public tbb::task
     bool _split; //"true" means a merge task is a split task for parallel merging, the execution logic differs
 
     bool
     is_partial() const
     {
         return _M_nsort > 0;
     }
 
-    struct move_value
+    struct __move_value
     {
         template <typename Iterator1, typename Iterator2>
         void
         operator()(Iterator1 __x, Iterator2 __z)
         {
             *__z = std::move(*__x);
         }
     };
 
-    struct move_value_construct
+    struct __move_value_construct
     {
         template <typename Iterator1, typename Iterator2>
         void
         operator()(Iterator1 __x, Iterator2 __z)
         {
             ::new (std::addressof(*__z)) _ValueType(std::move(*__x));
         }
     };
 
-    struct move_range
+    struct __move_range
     {
         template <typename Iterator1, typename Iterator2>
         Iterator2
         operator()(Iterator1 __first1, Iterator1 __last1, Iterator2 __first2)
         {
             if (__last1 - __first1 < __merge_cut_off)
                 return std::move(__first1, __last1, __first2);
 
             auto __n = __last1 - __first1;
             tbb::parallel_for(tbb::blocked_range<_SizeType>(0, __n, __merge_cut_off),
                               [__first1, __first2](const tbb::blocked_range<_SizeType>& __range) {
                                   std::move(__first1 + __range.begin(), __first1 + __range.end(),
                                             __first2 + __range.begin());
                               });
             return __first2 + __n;
         }
     };
 
-    struct move_range_construct
+    struct __move_range_construct
     {
         template <typename Iterator1, typename Iterator2>
         Iterator2
         operator()(Iterator1 __first1, Iterator1 __last1, Iterator2 __first2)
         {
             if (__last1 - __first1 < __merge_cut_off)
             {
                 for (; __first1 != __last1; ++__first1, ++__first2)
-                    move_value_construct()(__first1, __first2);
+                    __move_value_construct()(__first1, __first2);
                 return __first2;
             }
 
             auto __n = __last1 - __first1;
             tbb::parallel_for(tbb::blocked_range<_SizeType>(0, __n, __merge_cut_off),
                               [__first1, __first2](const tbb::blocked_range<_SizeType>& __range) {
                                   for (auto i = __range.begin(); i != __range.end(); ++i)
-                                      move_value_construct()(__first1 + i, __first2 + i);
+                                      __move_value_construct()(__first1 + i, __first2 + i);
                               });
             return __first2 + __n;
         }
     };
 
     struct __cleanup_range
     {
         template <typename Iterator>
merge_ranges()
 
             assert(is_partial() || std::is_sorted(_M_z_beg + _M_xs, _M_z_beg + _M_xe, _M_comp));
             assert(is_partial() || std::is_sorted(_M_z_beg + _M_ys, _M_z_beg + _M_ye, _M_comp));
 
             const auto __nx = (_M_xe - _M_xs);
             const auto __ny = (_M_ye - _M_ys);
 
             _M_leaf_merge(_M_z_beg + _M_xs, _M_z_beg + _M_xe, _M_z_beg + _M_ys, _M_z_beg + _M_ye, _M_x_beg + _M_zs,
-                          _M_comp, move_value(), move_value(), move_range(), move_range());
+                          _M_comp, __move_value(), __move_value(), __move_range(), __move_range());
 
             __cleanup_range()(_M_z_beg + _M_xs, _M_z_beg + _M_xe);
             __cleanup_range()(_M_z_beg + _M_ys, _M_z_beg + _M_ye);
         }
         return nullptr;
     }
 
     tbb::task*