Check libpng directly into third_party/

third_party/libpng/contrib/pngminus/makefile.tc3

Index: third_party/libpng/contrib/pngminus/makefile.tc3
diff --git a/third_party/libpng/contrib/pngminus/makefile.tc3 b/third_party/libpng/contrib/pngminus/makefile.tc3
new file mode 100644
index 0000000000000000000000000000000000000000..6a2f4b9853f8ad5d41253ad86299c51fccacbcf8
--- /dev/null
+++ b/third_party/libpng/contrib/pngminus/makefile.tc3
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+# Makefile for PngMinus (png2pnm and pnm2png)
+# TurboC++ 3.0
+
+CC=tcc -Ic:\tc3\inc
+LD=tcc -Lc:\tc3\lib
+LB=tlib
+RM=del
+CP=copy
+MODEL=l
+CPPFLAGS=-I..\libpng -I..\zlib
+CFLAGS=-O -m$(MODEL)
+LDFLAGS=-m$(MODEL) -L..\libpng -L..\zlib
+C=.c
+O=.obj
+L=.lib
+E=.exe
+
+# dependencies
+
+all: png2pnm$(E) pnm2png$(E)
+
+png2pnm$(O): png2pnm$(C)
+        $(CC) -c $(CPPFLAGS) $(CFLAGS) png2pnm$(C)
+
+png2pnm$(E): png2pnm$(O)
+        $(LD) $(LDFLAGS) png2pnm$(O) libpng$(L) zlib$(L)
+
+pnm2png$(O): pnm2png$(C)
+        $(CC) -c $(CPPFLAGS) $(CFLAGS) pnm2png$(C)
+
+pnm2png$(E): pnm2png$(O)
+        $(LD) $(LDFLAGS) pnm2png$(O) libpng$(L) zlib$(L)
+
+clean:
+        $(RM) *$(O)
+        $(RM) *$(E)
+
+# End of makefile for png2pnm / pnm2png