Hi,
this particular compilation issue is explained and fixed at https://github.com/root-project/root/pull/6912 .
However, as you say, ROOT is not tested on devtoolset (and some incompatibilities between ROOT’s C++ interpreter and devtoolsets are expected) so it’s not recommended to use ROOT+devtoolset.
Also see the discussion here for more context.
Cheers,
Enrico 