tools cpupower bench: Override CFLAGS assignments

Allow user to specify outside CFLAGS values as make argument

Corrects an issue where CFLAGS is passed as a make argument for
cpupower, but bench's makefile does not inherit and append to them.

Signed-off-by: Stanley Chan <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/power/cpupower/bench/Makefile

···
 OBJS = $(OUTPUT)main.o $(OUTPUT)parse.o $(OUTPUT)system.o $(OUTPUT)benchmark.o
 endif
 
-CFLAGS += -D_GNU_SOURCE -I../lib -DDEFAULT_CONFIG_FILE=\"$(confdir)/cpufreq-bench.conf\"
+override CFLAGS += -D_GNU_SOURCE -I../lib -DDEFAULT_CONFIG_FILE=\"$(confdir)/cpufreq-bench.conf\"
 
 $(OUTPUT)%.o : %.c
 	$(ECHO) "  CC      " $@