[libc++] Remove the c++98 Lit feature from the test suite
C++98 and C++03 are effectively aliases as far as Clang is concerned.
As such, allowing both std=c++98 and std=c++03 as Lit parameters is
just slightly confusing, but provides no value. It's similar to allowing
both std=c++17 and std=c++1z, which we don't do.
This was discovered because we had an internal bot that ran the test
suite under both c++98 AND c++03 -- one of which is redundant.
Differential Revision: https://reviews.llvm.org/D80926
diff --git a/libcxx/test/std/thread/thread.latch/count_down.pass.cpp b/libcxx/test/std/thread/thread.latch/count_down.pass.cpp
index 9374a6e..b411d86 100644
--- a/libcxx/test/std/thread/thread.latch/count_down.pass.cpp
+++ b/libcxx/test/std/thread/thread.latch/count_down.pass.cpp
@@ -7,7 +7,7 @@
//===----------------------------------------------------------------------===//
//
// UNSUPPORTED: libcpp-has-no-threads
-// UNSUPPORTED: c++98, c++03, c++11
+// UNSUPPORTED: c++03, c++11
// This test requires the dylib support introduced in D68480
// XFAIL: with_system_cxx_lib=macosx10.15