PHP Warning: PHP Startup: Unable to load dynamic library 'D:/AppServ\php7\ext\php_pdo_firebird.dll'

windows环境下cmd执行composer时出现警告：PHP Startup: Unable to load dynamic library php_pdo_firebird.dll：

$PHP Warning: PHP Startup: Unable to load dynamic library 'D:/AppServ\php7\ext\php_pdo_firebird.dll'$

但是php.ini中有关php_mysql.dll和php_pdo_firebird.dll扩展配置的部分都已经取消注释，php的安装目录中php_pdo_firebird.dll文件也能找到，此时下载fbclient.dll，把这个文件复制到php的安装根目录：

$PHP Warning: PHP Startup: Unable to load dynamic library 'D:/AppServ\php7\ext\php_pdo_firebird.dll'$

再次运行composer install未报错：

$PHP Warning: PHP Startup: Unable to load dynamic library 'D:/AppServ\php7\ext\php_pdo_firebird.dll'$