Both the MySQL and ereg functions were removed as part of PHP 7.
In order to bring them back, run the following:
yum groupinstall "Development Tools" -y
yum install rpmbuild autoconf automake curl libev libev-devel pcre pcre-devel perl udns-devel git -y
git clone https://github.com/php/pecl-database-mysql mysql --recursive
cd mysql
phpize
./configure
make
make install
echo "extension=mysql.so" >> /etc/php.d/20-mysqlnd.ini
cd ..
mkdir /ereg
cd /ereg
wget https://github.com/php/pecl-text-ereg/archive/master.zip
unzip master.zip
cd pecl-text-ereg-master
phpize
./configure
make
make install
echo "extension=ereg.so" > /etc/php.d/20-ereg.ini