Here are some commonly used commands for installing extension under php7.

Some extensions now support php7 in the stable versions:

phpbrew ext install apcu stable
phpbrew ext install xdebug stable
phpbrew ext install redis stable
phpbrew ext install memcached stable -- --disable-memcached-sasl

To install redis extension

phpbrew ext install github:phpredis/phpredis php7

To install APCu extension

phpbrew ext install github:krakjoe/apcu