I try to install zint 2.1.2 on my FreeBSD but it have some problem when compile.
This is my way to fix it.

{smartads}
If you need QR Code please install libqrencode-3.0.3 first

edit
backend/qr.c line 27
from:
#include <qrencode.h>
 
to:
#include "qrencode.h"

Copy header file
cp /usr/local/include/qrencode.h /YOUR.SOURCE.PATH/backend/
cp /usr/local/include/png.h /YOUR.SOURCE.PATH/backend/
cp /usr/local/include/pngconf.h /YOUR.SOURCE.PATH/backend/

edit
backend/Makefile line 53
from:
install -D -p --mode=0644 zint.h $(DESTDIR)$(includedir)/zint.h
 
to:
install -p -m 0644 zint.h $(DESTDIR)$(includedir)/zint.h
 
edit
frontend/Makefile line 28
from:
install -D -p  zint $(DESTDIR)$(bindir)/zint
 
to:
install -p  zint $(DESTDIR)$(bindir)/zint
 
cd /YOUR.SOURCE.PATH/
make
make install
 
or
gmake
gmake install