I have an application that needs to be build from source. It comes with 
a makefile (no configure script or anything like that.)  At the end of 
the build process, linking fails with the error pasted at the end.

How should the link command look for it to link against libpng 1.2 
rather than 1.4?  (I seem to have both installed.)

gcc -rdynamic -o sfrotz -Xlinker -Map -Xlinker mymap.map buffer.o err.o 
fastmem.o files.o getopt.o hotkey.o input.o main.o math.o object.o 
process.o quetzal.o random.o redirect.o screen.o sound.o stream.o 
table.o text.o variable.o blorblib.o sf_resource.o sf_images.o 
sf_fonts.o sf_sound.o sf_util.o sf_video.o sf_msg_en.o sf_deffont.o 
sf_font3.o sf_ftype.o sf_osfdlg.o sf_sig.o sf_aiffwav.o sf_resample.o 
-ljpeg -lpng -lz -lSDL -lSDL_mixer -lsamplerate `freetype-config --libs`
sf_images.o: In function `loadpng.clone.1':
sf_images.c:(.text+0x711): undefined reference to `png_set_gray_1_2_4_to_8'