Build utility apps -Os to save ROM space.

apps/examples/nsh/Makefile

apps/nshlib/Makefile

apps/px4/tests/Makefile

apps/system/i2c/Makefile

apps/systemcmds/bl_update/Makefile

apps/systemcmds/boardinfo/Makefile

apps/systemcmds/calibration/Makefile

apps/systemcmds/delay_test/Makefile

apps/systemcmds/eeprom/Makefile

apps/systemcmds/mixer/Makefile

apps/systemcmds/param/Makefile

apps/systemcmds/perf/Makefile

apps/systemcmds/preflight_check/Makefile

apps/systemcmds/reboot/Makefile

apps/systemcmds/top/Makefile