can't build dll with gnutls on Windows

I need a freetds dll that uses gnutls instead of openssl for an old Windows
application that uses db-library. All of the pre-built binaries I've found
use openssl instead of gnutls. I attempted to build it myself but
unfortunately I haven't been able to do so.

I am new to CMake but as best I can tell the CMakeLists.txt doesn't try to
locate the gnutls artifacts. So, I downloaded the gnutls windows binary
package, made some ugly hacks to the CMakeLists.txt file, and set the
CMAKE_PREFIX_PATH environment variable so that CMake appears to be locating
the gnutls artifacts. However, when I open the generated sln file in Visual
Studio 2013 and attempt to build the dll I get errors from gnutls.h that
seem to indicate that ssize_t is undefined. So I'm stuck at this point.

After getting stuck trying to use CMake I decided to try MingW. And when I
got stuck with MingW I tried Cygwin. My results with both MingW and Cygwin
were similar. I am unfamiliar with both of them and there appear to be a
lot of steps I'm missing between "download and install MingW (or Cygwin)"
and "build the freetds windows dll".

Can anyone point me in the right direction? I just need a freetds dll using
gnutls and its corresponding lib file so that I can rebuild my application
with Visual Studio. It doesn't matter much to me how I have to generate the
dll (CMake/MingW/Cygwin).

Thanks in advance.