Fix ROOT-8359: the first compiler we look for is the one the path
Fix ROOT-8359: the first compiler we look for is the one the path

then the one that was used to build cling and finally the one
in the absolute path (e.g. usr/bin/g++)

root-mirror/cling,karies/cling,root-mirror/cling,karies/cling,root-mirror/cling,root-mirror/cling,root-mirror/cling,karies/cling,karies/cling,karies/cling,karies/cling,root-mirror/cling