https://github.com/Rup0rt/pcapfix/pull/27

From: Sam James <sam@gentoo.org>
Date: Wed, 29 Dec 2021 06:48:09 +0000
Subject: [PATCH] build: respect CFLAGS

Allow overriding in the environment by using our value
as just a default.

Signed-off-by: Sam James <sam@gentoo.org>
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@ MANDIR ?= $(PREFIX)/share/man
 OPTFLAGS = $(shell getconf LFS_CFLAGS) -D_FORTIFY_SOURCE=2 -O2 -fstack-protector --param=ssp-buffer-size=4
 WARNFLAGS = -Wall -Wextra -std=gnu99 -pedantic -Wformat -Werror=format-security
 DEBUGFLAGS = -g
-CFLAGS += $(OPTFLAGS) $(WARNFLAGS) $(DEBUGFLAGS)
+CFLAGS ?= $(OPTFLAGS) $(WARNFLAGS) $(DEBUGFLAGS)
 
 # Determine extra LDFLAGS
 OS := $(shell uname)