Test: disable move-only-cxx-value-type.swift

The test was relying on UnsafeMutablePointer (UMP) not having a Copyable
 requirement. Those Copyable requirements are more prominent when using
the new infrastructure for noncopyable types. Since UMP is planned to
have `~Copyable` on its generic parameter quite soon, this shouldn't
remain broken for too long.

(cherry picked from commit 2951162)

Author: kavon

test/Interop/Cxx/class/move-only/move-only-cxx-value-type.swift

@@ -4,6 +4,9 @@
 //
 // REQUIRES: executable_test
 
+// Needs an UnsafeMutablePointer where Pointee: ~Copyable (rdar://124544696)
+// XFAIL: *
+
 import MoveOnlyCxxValueType
 import StdlibUnittest