[libcxx][test] Update msvc_stdlib_force_include.h for C++23

Make distinct `TEST_STD_VER` values for C++20 and C++23; add C++23 deprecation suppression.

Fixes #53597

libcxx/test/support/msvc_stdlib_force_include.h

@@ -69,18 +69,21 @@ const AssertionDialogAvoider assertion_dialog_avoider{};
     // Restore features that are removed in C++20.
     #define _HAS_FEATURES_REMOVED_IN_CXX20 1
 
-    // Silence warnings about features that are deprecated in C++17 and C++20.
+    // Silence warnings about features that are deprecated in non-default language modes.
     #define _SILENCE_ALL_CXX17_DEPRECATION_WARNINGS
     #define _SILENCE_ALL_CXX20_DEPRECATION_WARNINGS
+    #define _SILENCE_ALL_CXX23_DEPRECATION_WARNINGS
 #endif // _LIBCXX_IN_DEVCRT
 
 #include <version>
 
-#if _HAS_CXX20
+#if _HAS_CXX23
     #define TEST_STD_VER 99
+#elif _HAS_CXX20
+    #define TEST_STD_VER 20
 #elif _HAS_CXX17
     #define TEST_STD_VER 17
-#else // !(_HAS_CXX20 || _HAS_CXX17)
+#else
     #define TEST_STD_VER 14
 #endif