Enabling it in the relevant distro-configs/Jenkins/* file is more intuitive than
enabling it in autogen.sh (and avoids issues like
d057e61c "Restrict Developer Toolset to
Config=linux_gcc_release_64"), and will also be used for other Jenkins jobs like
<https://gerrit.libreoffice.org/#/c/63982/> "Enabling Developer Toolset 7 for
Jenkins' lo_tb_master_linux_dbg".

Change-Id: If633044a90c35a12a73d60335839af0a106aa20f
Reviewed-on: https://gerrit.libreoffice.org/63989
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>