What should I specify as CGIBIN_DIR in the Makefile ?
In most cases it is best to specify the global cgi-bin directory as the place to install the binary. This system administrator usually only has access to this place. However, if you are a user on a system and you would like to install the package in your local directory on the server, you have to make sure that it is possible to execute CGI-scripts in user-directories on your server (in most cases this is disabled; check with your system administrator). If it is possible to do that, most probably the binary has to have the extension .cgi. Just copy the resulting binary to nph-count.cgi.
