So, RedHat Enterprise Linux doesn't support the MCrpyt module, but you can get it from the Fedora project through the EPL. This would work fine, except the fact that we're using SoftWare Collections (SCL) to get a newer version of PHP (5.4).
So what is the best approach to getting the dependencies for laravell on RHEL 6.6 and keeping PHP 5.4 in the most vendor supported way possible?
About mcrypt, libmcrypt is a dead project, unmaintained for ~8 years, last version 2.5.8 was released in February 2007!... and despite lot of open tickets, no activity. Cryptography is a very important part of security management. Looking at the past, and issue discovered / fixed in various software, and the need to always increase security standards, and to drop old algorithms, how can we imagine using an 8 years old software ?
More, http://blog.remirepo.net/post/2015/07/07/About-libmcrypt-and-php-mcrypt
This explain why php-mcript is not part of RHEL/RHSCL official packages.
Additional packages for php54 collection (including php54-php-mcrypt) are available on https://www.softwarecollections.org/en/scls/remi/php54more/
And FYI, Laravel 5.1 doesn't requires mcrypt anymore.