Fix a test #ifdef that was reversed. NFC to the library.

llvm-svn: 336855
diff --git a/libcxx/test/std/strings/string.view/string.view.cons/assign.pass.cpp b/libcxx/test/std/strings/string.view/string.view.cons/assign.pass.cpp
index b7348ea..f31bc6d 100644
--- a/libcxx/test/std/strings/string.view/string.view.cons/assign.pass.cpp
+++ b/libcxx/test/std/strings/string.view/string.view.cons/assign.pass.cpp
@@ -41,7 +41,7 @@
 
 #if TEST_STD_VER > 11
     static_assert( test<std::string_view>    ({ "abc", 3}), "");
-#ifdef _LIBCPP_HAS_NO_UNICODE_CHARS
+#ifndef _LIBCPP_HAS_NO_UNICODE_CHARS
     static_assert( test<std::u16string_view> ({u"abc", 3}), "");
     static_assert( test<std::u32string_view> ({U"abc", 3}), "");
 #endif