cmake HAVE_GPIO_CDEV_V2 examples

brainflow-dev/brainflow third_party/periphery/CMakeLists.txt :12

check_source_compiles(C "#include <linux/gpio.h>\nint main(void) { GPIO_V2_LINE_FLAG_EVENT_CLOCK_REALTIME; return 0; }" HAVE_GPIO_CDEV_V2)