There's a sample makefile.gcc for pngcrush, which you can use
by typing

    make -f makefile.gcc

However, all you should need to do is enter the pngcrush-1.3.0
directory and type

    cc -O -o pngcrush *.c -lm
    cp pngcrush /usr/local/bin  # or wherever you want

You might want to create a makefile if you are planning to do
something more complicated, like loading with your system's shared
libraries for libpng and zlib.

Here's a command for compiling on SGI IRIX:

    cc -n32 -fullwarn -O2 -IPA:plimit=256 -OPT:Olimit=0 -o pngcrush *.c -lm
    cp pngcrush /usr/local/bin

On a PC with DJGCC, you can type

    gcc -O3 -Wall -funroll-loops -o pngcrush *.c
    copy /B pmodstub.exe + pngcrush pngcrush.exe

then put pngcrush.exe wherever you want.