Makefile: git diff with fetch_head works better with buildbot
Makefile: git diff with fetch_head works better with buildbot

RodolpheFouquet/gpac,gpac/gpac,rbouqueau/gpac,rbouqueau/gpac,RodolpheFouquet/gpac,RodolpheFouquet/gpac,rbouqueau/gpac,gpac/gpac,rbouqueau/gpac,rbouqueau/gpac,rbouqueau/gpac,gpac/gpac,rbouqueau/gpac,rbouqueau/gpac,gpac/gpac,gpac/gpac,gpac/gpac,gpac/gpac,RodolpheFouquet/gpac,RodolpheFouquet/gpac,RodolpheFouquet/gpac,gpac/gpac