Remove use of pthread_cancel in the swapchain page flip thread
The WSI layer may call pthread_cancel and kill the page flip thread while it's still being used in Vulkan-API calls. This can cause the layer to fail to clean up internal resources of the associated device, leading to memory leaks. To resolve this, the layer now instead checks if the page flip thread needs to end on every loop iteration. The m_page_flip_semaphore has also been changed to a timed_semaphore to avoid hanging indefinitely. In addition, m_page_flip_thread is now type std::thread, which follows the gradual move towards C++ standard code.
Change-Id: Iefbdd0d68e1f92fdf79bcebb7eaf33429fc61fd3 Signed-off-by: Dennis Tsiang email@example.com