During the installation, it may be needed to build locales that are not
covered by glibc-utf8-locales. Make sure that the libraries required to build
locales are available.
This is a follow-up of 0eed77127592323d89f56c215a15374a1aaae110.
* gnu/system/install.scm (installation-os)[services]: Add
%default-locale-libcs to gc-root-service-type.