[libc++][test] Update _LIBCPP_SUPPRESS_DEPRECATED_(PUSH|POP)

... in `msvc_stdlib_force_include.h` to also ignore new MSVC warning C5215 "'%s' a function parameter with volatile qualified type is deprecated in C++20". Since we're touching it, also update from non-standard `__pragma(meow)` to standard `_Pragma("meow")`.
diff --git a/libcxx/test/support/msvc_stdlib_force_include.h b/libcxx/test/support/msvc_stdlib_force_include.h
index 768558e..77d7222 100644
--- a/libcxx/test/support/msvc_stdlib_force_include.h
+++ b/libcxx/test/support/msvc_stdlib_force_include.h
@@ -100,10 +100,11 @@
     _Pragma("GCC diagnostic pop")
 #else // ^^^ clang / MSVC vvv
 #define _LIBCPP_SUPPRESS_DEPRECATED_PUSH \
-    __pragma(warning(push)) \
-    __pragma(warning(disable : 4996))
+    _Pragma("warning(push)") \
+    _Pragma("warning(disable : 4996)") \
+    _Pragma("warning(disable : 5215)")
 #define _LIBCPP_SUPPRESS_DEPRECATED_POP \
-    __pragma(warning(pop))
+    _Pragma("warning(pop)")
 #endif // __clang__
 
 #endif // SUPPORT_MSVC_STDLIB_FORCE_INCLUDE_H