Guard libc++ specific c.__invariants() tests in LIBCPP_ASSERT macros

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@267947 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/strings/basic.string/string.nonmembers/string.special/swap_noexcept.pass.cpp

@@ -7,6 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: c++98, c++03
+
 // <string>
 
 // void swap(basic_string& c)
@@ -22,6 +24,7 @@
 #include <string>
 #include <cassert>
 
+#include "test_macros.h"
 #include "test_allocator.h"
 
 template <class T>
@@ -51,7 +54,6 @@ struct some_alloc2
 
 int main()
 {
-#if __has_feature(cxx_noexcept)
     {
         typedef std::string C;
         C c1, c2;
@@ -80,6 +82,4 @@ int main()
         static_assert( noexcept(swap(c1, c2)), "");
     }
 #endif
-
-#endif
 }