move posix/tests/hello to examples/hello and include everywhere

boards/aerotenna/ocpoc/ubuntu.cmake

boards/airmind/mindpx-v2/default.cmake

boards/atlflight/excelsior/default.cmake

boards/atmel/same70xplained/default.cmake

boards/auav/x21/default.cmake

boards/av/x-v1/default.cmake

boards/beaglebone/blue/cross.cmake

boards/beaglebone/blue/native.cmake

boards/emlid/navio2/cross.cmake

boards/emlid/navio2/native.cmake

boards/nxp/hlite-v3/default.cmake

boards/px4/fmu-v2/default.cmake

boards/px4/fmu-v2/lpe.cmake

boards/px4/fmu-v2/test.cmake

boards/px4/fmu-v3/default.cmake

boards/px4/fmu-v3/rtps.cmake

boards/px4/fmu-v3/stackcheck.cmake

boards/px4/fmu-v4/default.cmake

boards/px4/fmu-v4/rtps.cmake

boards/px4/fmu-v4/stackcheck.cmake