Check libpng directly into third_party/

third_party/libpng/scripts/makefile.ne12bsd

+# makefile for libpng for NetBSD for the standard
+# make obj && make depend && make && make test
+# make includes && make install
+# Copyright (C) 2002 Patrick R.L. Welche
+# Copyright (C) 2007, 2009, 2014 Glenn Randers-Pehrson
+#
+# This code is released under the libpng license.
+# For conditions of distribution and use, see the disclaimer
+# and license in png.h
+
+# You should also run makefile.netbsd
+
+LOCALBASE?=/usr/local
+LIBDIR= ${LOCALBASE}/lib
+MANDIR= ${LOCALBASE}/man
+INCSDIR=${LOCALBASE}/include/libpng16
+
+LIB=    png16
+SHLIB_MAJOR=    0
+SHLIB_MINOR=    1.6.22rc01
+SRCS=   png.c pngset.c pngget.c pngrutil.c pngtrans.c pngwutil.c \
+        pngread.c pngrio.c pngwio.c pngwrite.c pngrtran.c \
+        pngwtran.c pngmem.c pngerror.c pngpread.c
+INCS=   png.h pngconf.h pnglibconf.h
+MAN=    libpng.3 libpngpf.3 png.5
+
+CPPFLAGS+=-I${.CURDIR}
+
+# Pre-built configuration
+# See scripts/pnglibconf.mak for more options
+PNGLIBCONF_H_PREBUILT= scripts/pnglibconf.h.prebuilt
+
+# We should be able to do something like this instead of the manual
+# uncommenting, but it core dumps for me at the moment:
+# .if ${MACHINE_ARCH} == "i386"
+#   MKLINT= no
+# .endif
+
+CLEANFILES+=pngtest.o pngtest pnglibconf.h
+
+.c.o:
+        $(CC) -c $(CPPFLAGS) $(CFLAGS) -o $@ $<
+
+pnglibconf.h: $(PNGLIBCONF_H_PREBUILT)
+        cp $(PNGLIBCONF_H_PREBUILT) $@
+
+pngtest.o:      pngtest.c
+        ${CC} -c ${CPPFLAGS} ${CFLAGS} ${.ALLSRC} -o ${.TARGET}
+
+pngtest:        pngtest.o libpng.a
+        ${CC} ${LDFLAGS} ${.ALLSRC} -o${.TARGET} -lz -lm
+
+test:   pngtest
+        cd ${.CURDIR} && ${.OBJDIR}/pngtest
+
+.include <bsd.lib.mk>