AC_AutoTune: use new new macro #910

Job	Run time
build (base)	2m 14s
build (clang)	2m 16s
build-gcc-heli	2m 9s
autotest-heli (sitltest-heli)	10m 25s
autotest (sitltest-copter-tests1a)	7m 20s
autotest (sitltest-copter-tests1b)	9m 11s
autotest (sitltest-copter-tests1c)	10m 59s
autotest (sitltest-copter-tests1d)	7m 53s
autotest (sitltest-copter-tests1e)	8m 50s
autotest (sitltest-copter-tests2a)	9m 5s
autotest (sitltest-copter-tests2b)	26m 15s
	1h 36m 37s

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