build: Exit with return code in update_external bat
build: Exit with return code in update_external bat

Change-Id: Idf9d85d36c66a63de0c07322a367b45cfe84e3de

KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers