compiling PHP 7.1.8



I use php as a language base for a website with Drupal, Symfony, MySQL, Apache, running Debian 9 (Stretch). I now tried to upgrad PHP to v 7.1.8. Since Debian Stretch doesn't yet include PHP 7.1.8, I am trying to build it from source. This obviously being a complex environment, it is maybe why my experience during the past few days ressembles a nightmare. In any case I simply cannot get things to run. My config parameters are as follows:
./configure --with-gd --with-mcrypt --with-mhash --with-mysqli=mysqlnd --enable-mysqlnd --with-pdo-mysql=mysqlnd --with-mysql-sock=/var/run/mysqld/mysqld.sock --enable-pdo --enable-soap --with-config-file-path=/etc/php/7.1.8/apache2 --with-config-file-scan-dir=/etc/php/7.1.8/apache2/conf.d --enable-bcmath --with-zlib --with-zlib-dir=/lib/x86_64-linux-gnu --with-readline --enable-mbstring --prefix=/opt/php-7.1.8 --with-jpeg-dir=/usr/lib --with-png-dir=/usr/lib --with-openssl --with-openssl-dir=/usr/bin --with-curl=/usr/local --enable-debug
When I now try to run the command php -v, after "make install" I get the following response:
PHP Warning: PHP Startup: Unable to load dynamic library '/usr/lib/php/20160303/' - /usr/lib/php/20160303/ undefined symbol: EVP_SignFinal in Unknown on line 0
PHP 7.1.8 (cli) (built: Aug 7 2017 15:20:15) ( NTS )
Copyright (c) 1997-2017 The PHP Group
Zend Engine v3.1.0, Copyright (c) 1998-2017 Zend Technologies
It also seems that the configure-options --with-config-file-path=/etc/php/7.1.8/apache2 --with-config-file-scan-dir=/etc/php/7.1.8/apache2/conf.d
don't have any effect on the built system. I have to set the path for php.ini by exporting the relevant file. I wonder what I am missing.
Thanks for any hints
H. Stoellinger