The minimum set of Cygwin packages needed to build wc3270 are:
[optional] If you want SSL support, you will need to build a MinGW OpenSSL library. That requres the following packages:
cd /usr/src/openssl-* ./Configure --prefix=/usr/local/mingw-openssl mingw make make install
To build wc3270 (with or without SSL support), start a Cygwin shell, cd to the directory where the source code resides, and type:
makewc3270 was developed primarily on 32-bit Windows XP, but should be buildable on Windows Server 2003 or Windows 2000 (though Windows 2000 has been known to build defective wc3270 DLLs). It has not been built on 64-bit Windows or on Windows Vista.
The source tarball also includes an .iss file for use with Inno Setup. This is used to construct the install executable. See the Inno Setup webpage for details.
wc3270 can also be built on Linux, using the MinGW cross-compiler. (This is how public releases of wc3270 are built.) The precise method for building a cross-compiler varies with gcc, Binutils and MinGW releases, but this link should get you started.