[libc++][test] Replace `_LIBCPP_STD_VER` with `TEST_STD_VER`

[philnik]

Do you need someone to commit it on your behalf?

[cpplearner]

In D130979#3693222, @philnik wrote:

Do you need someone to commit it on your behalf?

Yes, I do.

My name and email address: Tan S. B. <[e-mail]>

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_convert_copy.pass.cpp

struct Explicit {
   explicit Explicit(int x) : value(x) {}
 };
 
 struct Implicit {
   int value;
   Implicit(int x) : value(x) {}
 };
 
-#if _LIBCPP_STD_VER > 17
+#if TEST_STD_VER > 17
 constexpr bool alloc_copy_constructor_is_constexpr() {
   const std::tuple<int> t1 = 1;
   std::tuple<int> t2 = {std::allocator_arg, test_allocator<int>{}, t1};
   assert(std::get<0>(t2) == 1);
   return true;
 }
 #endif
 
int main(int, char**)
     {
         // Test that we can use a tag derived from allocator_arg_t
         struct DerivedFromAllocatorArgT : std::allocator_arg_t { };
         DerivedFromAllocatorArgT derived;
         std::tuple<long> from(3l);
         std::tuple<long long> t0(derived, A1<int>(), from);
     }
 
-#if _LIBCPP_STD_VER > 17
+#if TEST_STD_VER > 17
     static_assert(alloc_copy_constructor_is_constexpr());
 #endif
     return 0;
 }

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_convert_move.pass.cpp

struct Explicit {
   explicit Explicit(int x) : value(x) {}
 };
 
 struct Implicit {
   int value;
   Implicit(int x) : value(x) {}
 };
 
-#if _LIBCPP_STD_VER > 17
+#if TEST_STD_VER > 17
 constexpr bool alloc_move_constructor_is_constexpr() {
   std::tuple<int> t1 = 1;
   std::tuple<int> t2 = {std::allocator_arg, test_allocator<int>{}, std::move(t1)};
   assert(std::get<0>(t2) == 1);
   return true;
 }
 #endif
 
int main(int, char**)
     {
         // Test that we can use a tag derived from allocator_arg_t
         struct DerivedFromAllocatorArgT : std::allocator_arg_t { };
         DerivedFromAllocatorArgT derived;
         std::tuple<long> from(3l);
         std::tuple<long long> t0(derived, A1<int>(), std::move(from));
     }
 
-#if _LIBCPP_STD_VER > 17
+#if TEST_STD_VER > 17
     static_assert(alloc_move_constructor_is_constexpr());
 #endif
 
     return 0;
 }

libcxx/test/support/test_iterators.h

public:
     TEST_CONSTEXPR_CXX14 cpp17_output_iterator& operator++() {++it_; return *this;}
     TEST_CONSTEXPR_CXX14 cpp17_output_iterator operator++(int) {return cpp17_output_iterator(it_++);}
 
     friend TEST_CONSTEXPR It base(const cpp17_output_iterator& i) { return i.it_; }
 
     template <class T>
     void operator,(T const &) = delete;
 };
-#if _LIBCPP_STD_VER > 17
+#if TEST_STD_VER > 17
    static_assert(std::output_iterator<cpp17_output_iterator<int*>, int>);
 #endif
 
 // This iterator meets C++20's Cpp17InputIterator requirements, as described
 // in Table 89 ([input.iterators]).
 template <class It, class ItTraits = It>
 class cpp17_input_iterator
 {
public:
     friend TEST_CONSTEXPR bool operator==(const cpp17_input_iterator& x, const cpp17_input_iterator& y) {return x.it_ == y.it_;}
     friend TEST_CONSTEXPR bool operator!=(const cpp17_input_iterator& x, const cpp17_input_iterator& y) {return x.it_ != y.it_;}
 
     friend TEST_CONSTEXPR It base(const cpp17_input_iterator& i) { return i.it_; }
 
     template <class T>
     void operator,(T const &) = delete;
 };
-#if _LIBCPP_STD_VER > 17
+#if TEST_STD_VER > 17
    static_assert(std::input_iterator<cpp17_input_iterator<int*>>);
 #endif
 
 template <class It>
 class forward_iterator
 {
     It it_;
 

libcxx/test/support/test_range.h

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 #ifndef LIBCXX_TEST_SUPPORT_TEST_RANGE_H
 #define LIBCXX_TEST_SUPPORT_TEST_RANGE_H
 
 #include <iterator>
 #include <ranges>
 
 #include "test_iterators.h"
 
-#if _LIBCPP_STD_VER < 17
+#if TEST_STD_VER < 17
 #error "test/support/test_range.h" can only be included in builds supporting ranges
 #endif
 
 struct sentinel {
   bool operator==(std::input_or_output_iterator auto const&) const;
 };
 
 template <template <class...> class I>