We do, in fact, support PHP extensions like GMP and Mcrypt.
Please get in touch with support if you have any special requirements or need a special configuration.
PHP provides two years of full support following the stable release of each release branch.
During this time, reported bugs and security issues are fixed and included in routine point releases. Each branch is supported for one more year for critical security issues following this two-year active support period.
Releases during this time are made as needed; depending on the volume of reports, there may be several point releases or none.
The branch reaches its end and is no longer supported after the three years are up.