duplicated c17 tests in c2x

Author: Aidan

clang/test/Sema/nullptr.c

@@ -112,4 +112,6 @@ void test_f1() {
 void foo(void *);
 void bar() { foo(__nullptr); }
 static_assert(nullptr == __nullptr);
+static_assert(__nullptr == 0);  // Test that its value matches that of NULL
 static_assert(_Generic(typeof(__nullptr), nullptr_t: true, default: false));
+static_assert(_Generic(__typeof(__nullptr), int : 0, void * : 0, default : 1)); // Test that it's type is not the same as what NULL would generally have.