I use version 1.2.7 with mingw. For compiling libssh2, there's a win32 sub dir containing Makefile for mingw. You need to edit file Makefile.win32 to adjust it according your installation: Compile with zlib, path, path to openssl and so on. For compiling libssh2 there's no need for qmake. Just run your make utility in win32 directory.
After successful compilation copy libraries, dlls and include files to your compiler installation and then you can use it in your Qt projects as you would do with any other external library.