[libcxx] Refactoring SIMD function names in PSTL CPU backend (#69029)

This PR addresses a smaller detail discussed in the code review for
#66968. Currently, some
functions in the `libc++` PSTL CPU backend have been appended with a
digit to indicate the number of input iterator arguments. However, there
is no need to change the name for each version as overloading can be
used instead. This PR will make the naming more consistent in the the
CPU and the proposed OpenMP backend.

libcxx/include/__algorithm/pstl_backends/cpu_backends/for_each.h

@@ -26,7 +26,7 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Iterator, class _DifferenceType, class _Function>
-_LIBCPP_HIDE_FROM_ABI _Iterator __simd_walk_1(_Iterator __first, _DifferenceType __n, _Function __f) noexcept {
+_LIBCPP_HIDE_FROM_ABI _Iterator __simd_walk(_Iterator __first, _DifferenceType __n, _Function __f) noexcept {
   _PSTL_PRAGMA_SIMD
   for (_DifferenceType __i = 0; __i < __n; ++__i)
     __f(__first[__i]);
@@ -47,7 +47,7 @@ __pstl_for_each(__cpu_backend_tag, _ForwardIterator __first, _ForwardIterator __
         });
   } else if constexpr (__is_unsequenced_execution_policy_v<_ExecutionPolicy> &&
                        __has_random_access_iterator_category_or_concept<_ForwardIterator>::value) {
-    std::__simd_walk_1(__first, __last - __first, __func);
+    std::__simd_walk(__first, __last - __first, __func);
     return __empty{};
   } else {
     std::for_each(__first, __last, __func);

libcxx/include/__algorithm/pstl_backends/cpu_backends/transform.h

@@ -32,7 +32,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Iterator1, class _DifferenceType, class _Iterator2, class _Function>
 _LIBCPP_HIDE_FROM_ABI _Iterator2
-__simd_walk_2(_Iterator1 __first1, _DifferenceType __n, _Iterator2 __first2, _Function __f) noexcept {
+__simd_walk(_Iterator1 __first1, _DifferenceType __n, _Iterator2 __first2, _Function __f) noexcept {
   _PSTL_PRAGMA_SIMD
   for (_DifferenceType __i = 0; __i < __n; ++__i)
     __f(__first1[__i], __first2[__i]);
@@ -60,7 +60,7 @@ _LIBCPP_HIDE_FROM_ABI optional<_ForwardOutIterator> __pstl_transform(
   } else if constexpr (__is_unsequenced_execution_policy_v<_ExecutionPolicy> &&
                        __has_random_access_iterator_category_or_concept<_ForwardIterator>::value &&
                        __has_random_access_iterator_category_or_concept<_ForwardOutIterator>::value) {
-    return std::__simd_walk_2(
+    return std::__simd_walk(
         __first,
         __last - __first,
         __result,
@@ -73,7 +73,7 @@ _LIBCPP_HIDE_FROM_ABI optional<_ForwardOutIterator> __pstl_transform(
 }
 
 template <class _Iterator1, class _DifferenceType, class _Iterator2, class _Iterator3, class _Function>
-_LIBCPP_HIDE_FROM_ABI _Iterator3 __simd_walk_3(
+_LIBCPP_HIDE_FROM_ABI _Iterator3 __simd_walk(
     _Iterator1 __first1, _DifferenceType __n, _Iterator2 __first2, _Iterator3 __first3, _Function __f) noexcept {
   _PSTL_PRAGMA_SIMD
   for (_DifferenceType __i = 0; __i < __n; ++__i)
@@ -116,7 +116,7 @@ _LIBCPP_HIDE_FROM_ABI optional<_ForwardOutIterator> __pstl_transform(
                        __has_random_access_iterator_category_or_concept<_ForwardIterator1>::value &&
                        __has_random_access_iterator_category_or_concept<_ForwardIterator2>::value &&
                        __has_random_access_iterator_category_or_concept<_ForwardOutIterator>::value) {
-    return std::__simd_walk_3(
+    return std::__simd_walk(
         __first1,
         __last1 - __first1,
         __first2,