implement ftruncate for gekko

ftruncate(int fd, off_t length) {

    debug_info("[BYPASS] >> Begin ftruncate.... %d %ld\n", fd, length);

    // gekko ftruncate

     if(CTX->interception_enabled()) {

    if(CTX->file_map()->exist(fd)) {

        debug_info("[FTRUNCATE from GKFS]....%d %ld\n", fd, length);

        return gkfs::syscall::gkfs_ftruncate(fd, length);

    }

     }

    int ret = dlsym_ftruncate(fd, length);