Same reversed ifdef happened twice. Test fix only, NFC to the library.

llvm-svn: 336856
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 f31bc6d..478bec7 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
@@ -33,7 +33,7 @@
 int main () {
 
     assert( test<std::string_view>    ( "1234"));
-#ifdef _LIBCPP_HAS_NO_UNICODE_CHARS
+#ifndef _LIBCPP_HAS_NO_UNICODE_CHARS
     assert( test<std::u16string_view> (u"1234"));
     assert( test<std::u32string_view> (U"1234"));
 #endif