[libc++] Precise XFAIL for AppleClang 11

This test doesn't fail on all patch levels of AppleClang 11

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@369420 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/meta/meta.rel/is_base_of_union.pass.cpp

@@ -18,7 +18,7 @@
 //  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, apple-clang-11
+// XFAIL: apple-clang-9.0, apple-clang-9.1, apple-clang-10.0, apple-clang-11.0.0
 // 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