You need to get Info-Zip's unzip540.zip from one of many
mirrors, and unzip it in this directory, with say

	unzip unzip540.zip -d unzip

Then alter UNZIPDIR in the Makefile if necessary and run make.

dounzip.c is based rather loosely on the windll/example.c file.

For some versions of the mingw32 headers you need to edit 
unzip/win32/win32.c and add #undef HAVE_INT64 at about line 532.