Add Mac OS X build product to gitignore
Fix unused variable / value warnings when building with clang

    fs.c:3175:37: warning: expression result unused [-Wunused-value]
                    for (i = 0; i < bytes_read1; i++, bytes_total) {
                                                      ^~~~~~~~~~~

    EX_browser_ping.c:347:11: warning: unused variable 'arg' [-Wunused-variable]
        u_int arg;
              ^

    cl_demo.c:3157:8: warning: unused variable 'asp' [-Wunused-variable]
            float asp = 0;
                  ^

    gl_rmain.c:1529:16: warning: unused variable 'gl_hwblend' [-Wunused-variable]
            extern cvar_t gl_hwblend;
                          ^