Set ICU_DATA to the right path to make Charlock Holmes and libicu work properly
Since --with-data-packaging=files
is used to install libicu, ICU_DATA needs
to be set or libicu will fail with U_FILE_ACCESS_ERROR
when attempting
certain conversions. See http://userguide.icu-project.org/icudata for more
details.
Closes gitlab-org/gitlab-ce#17415