[libc++] Temporarily disable failing test for Android CI runners

This test is currently failing in the Android CI, since the compiler
used there is too old. Once the Clang version is updated this XFAIL
should be removed again.

libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/has_unique_object_representations.compile.pass.cpp

diff --git a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/has_unique_object_representations.compile.pass.cpp b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/has_unique_object_representations.compile.pass.cpp
index bd7da40..9aac871 100644
--- a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/has_unique_object_representations.compile.pass.cpp
+++ b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/has_unique_object_representations.compile.pass.cpp
@@ -8,6 +8,9 @@
 
 // UNSUPPORTED: c++03, c++11, c++14
 
+// The Clang version that Android currently uses in the CI is too old.
+// XFAIL: LIBCXX-ANDROID-FIXME
+
 // type_traits
 
 // has_unique_object_representations