Add futures.unique_future/wait.pass.cpp to the skip lists (#641)

tests/libcxx/expected_results.txt

@@ -733,6 +733,7 @@ std/thread/futures/futures.async/async.pass.cpp SKIP
 std/thread/futures/futures.shared_future/get.pass.cpp SKIP
 std/thread/futures/futures.shared_future/wait_for.pass.cpp SKIP
 std/thread/futures/futures.unique_future/wait_for.pass.cpp SKIP
+std/thread/futures/futures.unique_future/wait.pass.cpp SKIP
 std/thread/thread.condition/thread.condition.condvar/notify_all.pass.cpp SKIP
 std/thread/thread.condition/thread.condition.condvar/notify_one.pass.cpp SKIP
 std/thread/thread.condition/thread.condition.condvar/wait_for_pred.pass.cpp SKIP

tests/libcxx/skipped_tests.txt

@@ -733,6 +733,7 @@ thread\futures\futures.async\async.pass.cpp
 thread\futures\futures.shared_future\get.pass.cpp
 thread\futures\futures.shared_future\wait_for.pass.cpp
 thread\futures\futures.unique_future\wait_for.pass.cpp
+thread\futures\futures.unique_future\wait.pass.cpp
 thread\thread.condition\thread.condition.condvar\notify_all.pass.cpp
 thread\thread.condition\thread.condition.condvar\notify_one.pass.cpp
 thread\thread.condition\thread.condition.condvar\wait_for_pred.pass.cpp