[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

@@ -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