Adjust unsupported C++ versions in some tests

Summary:
Some tests (mainly the new C++20 calendar library) fail when libc++ is
tested with '--param=std=c++98'. The failures happen because the tests
actually don't support C++98, but don't mention C++98 in the
'UNSUPPORTED:' line.

This change fixes the issue.

Reviewers: mclow.lists, ldionne

Reviewed By: ldionne

Subscribers: arphaman, michaelplatings, libcxx-commits

Differential Revision: https://reviews.llvm.org/D53640

llvm-svn: 345148
diff --git a/libcxx/test/std/utilities/time/weeks.pass.cpp b/libcxx/test/std/utilities/time/weeks.pass.cpp
index 6099d55..8e6f283 100644
--- a/libcxx/test/std/utilities/time/weeks.pass.cpp
+++ b/libcxx/test/std/utilities/time/weeks.pass.cpp
@@ -6,7 +6,7 @@
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
-// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
 
 // <chrono>