Keep upstream's important CFLAGS and macros and respect LDFLAGS. Omit those
which the toolchain sets for us:
https://wiki.gentoo.org/wiki/Hardened/Toolchain#Changes

From: Lucio Sauer <watermanpaint@posteo.net>
--- a/Makefile
+++ b/Makefile
@@ -2,13 +2,6 @@
 
 CFLAGS ?= -std=c11 -O2 -pipe -finline-functions -fPIC -Wall -Wextra -Wpedantic -Wfatal-errors
 UNAME_S := $(shell uname -s)
-ifeq ($(UNAME_S),Darwin)
-	CFLAGS += -fstack-protector-strong -D_GNU_SOURCE -fno-plt
-else ifeq ($(OS),Windows_NT)
-	CFLAGS += -D_WIN32
-else
-	CFLAGS += -fstack-protector-strong -D_GNU_SOURCE -fno-plt -Wl,-z,now
-endif
 
 PREFIX ?= /usr
 BINDIR ?= $(PREFIX)/bin
@@ -20,7 +13,7 @@
 RELEASE_FILES := main.c Makefile COPYING README.md
 
 tinyxxd: main.c
-	$(CC) $(CFLAGS) -o $@ $<
+	$(CC) $(CFLAGS) -std=c11 -D_GNU_SOURCE $(LDFLAGS) -o $@ $<
 
 tinyxxd_debug: main.c
 	$(CC) $(CFLAGS) -g -o $@ $<