targets O3 flags for arm and thumber targets

Change-Id: Ia760dd20be004fc29b2783911e346a338e58c10f
No errors on strict overflow

Wno-strict-overflow prevents the compilers to stop its compilation upon strict overflow

Change-Id: I5483325133002ab44034198c3f784f299e74cfd1

Conflicts:
	core/combo/TARGET_linux-arm.mk