master failing to build on centos6 due to charlock_holmes

Centos6 builds are currently failing after the charlock_holmes update in: !20546 (merged)

The error while running bundle install is:

cc1plus: error: unrecognized command line option "-std=c++11"
5587 make: *** [transliterator.o] Error 1
5588 make failed, exit code 2

Can be seen from builds here: https://dev.gitlab.org/gitlab/omnibus-gitlab/-/jobs/5926166

cc\ @stanhu cc\ @gitlab-org/distribution