MinGW provides libopengl32 and libglu, which are Windows equivalents of libGL and libGLU. With the attached patch ftgl compiles successfully (actually, it's a diff, not a patch; how do i create a patch for a source tree tracked by svn? something like git format-patch?).
A diff file is a proper patch, thanks. There were two typos in your patch, but I fixed them and applied it upstream.