To build Shrinkler natively for your unix-like system, type

make

You can cross-build for a particular target using

make PLATFORM=<platform>

where <platform> is one of:

amiga:      build for Amiga (build on Cygwin, and see below)
windows-32: build for 32-bit Windows (build on Cygwin)
windows-64: build for 64-bit Windows (build on Cygwin)
native:     same as default
native-32:  native, forced to 32 bits
native-64:  native, forced to 64 bits

To build for Amiga, you will first need to download a few things:

Download
http://amiga.sourceforge.net/phps/logger.php?download=GCC-4.5.0-m68k-amigaos-cygwin.7z
and unpack it to the toolchain directory.

Download
http://sourceforge.net/projects/amiga/files/Compilers/related/include-20090222.lha
and unpack it to the toolchain directory.

Create the directory toolchain/ixemul-sdk, download
http://sourceforge.net/projects/amiga/files/ixemul.library/48.2/ixemul-sdk.lha
and unpack it to the directory you just created.

The Amiga version will need ixemul.library version 48 or later to run.

Enjoy!