[libc++] Add XFAIL for is_base_of test on AppleClang 11

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@369280 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/std/utilities/meta/meta.rel/is_base_of_union.pass.cpp b/test/std/utilities/meta/meta.rel/is_base_of_union.pass.cpp
index 11a9afb..cfe2c30 100644
--- a/test/std/utilities/meta/meta.rel/is_base_of_union.pass.cpp
+++ b/test/std/utilities/meta/meta.rel/is_base_of_union.pass.cpp
@@ -14,11 +14,11 @@
 
 #include "test_macros.h"
 
-//  Clang before v9 and apple-clang up to and including v10 do not
+//  Clang before v9 and apple-clang up to and including v11 do not
 //  report that unions are never base classes - nor can they have bases.
 //  See https://reviews.llvm.org/D61858
 // XFAIL: apple-clang-6.0, apple-clang-7.0, apple-clang-8.0
-// XFAIL: apple-clang-9.0, apple-clang-9.1, apple-clang-10.0
+// XFAIL: apple-clang-9.0, apple-clang-9.1, apple-clang-10.0, apple-clang-11
 // XFAIL: clang-3.3, clang-3.4, clang-3.5, clang-3.6, clang-3.7, clang-3.8, clang-3.9
 // XFAIL: clang-4.0, clang-5.0, clang-6.0, clang-7.0, clang-8.0