Currently only SLES and openSUSE has GCC in versions.txt.
Will also make GCC versions visible in Tools and Versions pages.
Task-number: QTQAINFRA-5901
Pick-to: 6.9 6.8 6.5
Change-Id: I9742c3151e074c503947018a0c7f7c2e0c1077bd
Reviewed-by: Ville-Pekka Karhu <ville-pekka.karhu@qt.io>