Install missing libmhash and libmcrypt on CentOS 6 or RHEL 6

I recently began making the migration to RHEL 6. So far so good, except for a few unexpected hurdles. One of these was installing PHP on my web servers. The issue is that libmcrypt and libmhash cannot be found in the default repositories. When I attempted to build PHP, I received the following error:

configure: error: mcrypt.h not found. Please reinstall libmcrypt

Attempting to install libmcrypt-devel with only the default repositories installed will lead to a frustrating ‘nothing to do’ result from yum.

The only solution that I have found short of compiling libmcrypt from source, is to install the EPEL repositories. EPEL to the rescue!

rpm -ivh http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-5.noarch.rpm
Once installed, ‘yum install libmcrypt-devel’ will work as expected and you can continue with your configuration.