I was testing the new Debian "buster" image by @RobertCNelson and we noticed that the Adafruit_BBIO build was failing on compiler warnings. This seems to be due to the introduction of new compiler warnings in the more recent version of gcc that is on the buster image: https://rcn-ee.net/rootfs/bb.org/testing/2019-03-03/buster-iot/bone-debian-buster-iot-armhf-2019-03-03-4gb.img.xz a shot

NOTE: commit 0923b85 caused a regression in older versions of gcc. See issue #307

TODO: determine how to avoid compile failure in gcc 8.2.0 without causing a regression for gcc 6.3.0 in the current Debian 9.x "Stretch" images