fix compile for MacOSX -DFORTIFY_SOURCE=2 is problematic
diff --git a/GNUmakefile b/GNUmakefile
index 0cbeaa8..a2a4bca 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -54,6 +54,7 @@
  ifeq "$(shell echo 'int main() {return 0; }' | $(CC) $(CFLAGS) -Werror -x c - -march=native -o .test 2>/dev/null && echo 1 || echo 0 ; rm -f .test )" "1"
 	CFLAGS_OPT = -march=native
  endif
+	CFLAGS_OPT += -D_FORTIFY_SOURCE=2
 endif
 
 ifneq "$(shell uname -m)" "x86_64"
@@ -66,7 +67,7 @@
  endif
 endif
 
-CFLAGS     ?= -O3 -funroll-loops $(CFLAGS_OPT) -D_FORTIFY_SOURCE=2
+CFLAGS     ?= -O3 -funroll-loops $(CFLAGS_OPT)
 override CFLAGS += -Wall -g -Wno-pointer-sign \
 			  -I include/ -Werror -DAFL_PATH=\"$(HELPER_PATH)\" \
 			  -DBIN_PATH=\"$(BIN_PATH)\" -DDOC_PATH=\"$(DOC_PATH)\"