cpu/samd21: remove -O0 override
@ -6,7 +6,4 @@ export CFLAGS += -DDONT_USE_CMSIS_INIT
# use the hwtimer compatibility layer
USEMODULE += hwtimer_compat
# TODO: remove once the CPU implementation is stable with -Os
CFLAGS_OPT = -O0
include $(RIOTCPU)/Makefile.include.cortexm_common