Replace __cplusplus comparisons and dialect __has_feature checks with TEST_STD_VER.

This is a huge cleanup that helps make the libc++ test suite more portable.
Patch from STL@microsoft.com. Thanks STL!


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@272716 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/function.objects/func.memfn/member_function.pass.cpp

@@ -15,6 +15,8 @@
 #include <functional>
 #include <cassert>
 
+#include "test_macros.h"
+
 struct A
 {
     char test0() {return 'a';}
@@ -69,7 +71,7 @@ int main()
     test0(std::mem_fn(&A::test0));
     test1(std::mem_fn(&A::test1));
     test2(std::mem_fn(&A::test2));
-#if __has_feature(cxx_noexcept)
+#if TEST_STD_VER >= 11
     static_assert((noexcept(std::mem_fn(&A::test0))), ""); // LWG#2489
 #endif
 }