Test that queues are flushed by clReleaseCommandQueue (#923)

... as required by the OpenCL specification.

Also introduce a utility function to manage polling for changes
via a user-supplied function. Several tests we introduced lately
could have used this.

Signed-off-by: Kévin Petit <kpet@free.fr>

test_conformance/api/CMakeLists.txt

@@ -23,6 +23,7 @@ set(${MODULE_NAME}_SOURCES
          test_kernel_arg_info_compatibility.cpp
          test_null_buffer_arg.cpp
          test_mem_object_info.cpp
+         test_queue.cpp
          test_queue_hint.cpp
          test_queue_properties.cpp
          test_sub_group_dispatch.cpp