make: allow default distro definition of CFLAGS
make non-required CFLAGS optional if none are defined from the env
like in distro builds.
@@ -4,7 +4,8 @@ INSTALLDIR = $(DESTDIR)$(PREFIX)/bin
HOSTOS := $(shell uname -s)
CC ?= gcc
-CFLAGS = -std=gnu99 -O3 -Wall -Wextra
+CFLAGS ?= -O3 -Wall -Wextra
+CFLAGS += -std=gnu99
INSTFLAGS = -m 0755
ifeq ($(HOSTOS), Linux)
