Fix issue with PEAR's php_ini config.
Fix issue with PEAR's php_ini config.

The config was set for the user in ~/.pearrc and was overwritten by each
new PHP version installed: the value pointed to the php.ini of the last
PHP version installed.

The solution was to set the config for the "system layer" which is
version specific in our case.

hirak/php-build,php-build/php-build,hnw/php-build,stof/php-build,rogeriopradoj/php-build,gerardroche/php-build,0livier/php-build,circleci/php-build,stof/php-build,michael-berlin/php-build