3.2.7: ROOT requires support for C++17 or higher.

Using sci-physics/root-6.32.00 Gentoo CI complains:

from /usr/include/root/Compression.h:15,
                 from /usr/include/root/TFile.h:27,
                 from /var/tmp/portage/sci-physics/hepmc-3.2.7/work/HepMC3-3.2.7/rootIO/src/WriterRoot.cc:16:
/usr/include/root/RConfigure.h:30:4: warning: #warning "The C++ standard in this build does not match ROOT configuration (201703L); this might cause unexpected issues" [-Wcpp]
   30 | #  warning "The C++ standard in this build does not match ROOT configuration (201703L); this might cause unexpected issues"
      |    ^~~~~~~
/usr/include/root/ROOT/RConfig.hxx:48:2: error: #error "ROOT requires support for C++17 or higher."
   48 | #error "ROOT requires support for C++17 or higher."
      |  ^~~~~

Should the HepMC CMake maybe pick up how root was configured, if it is available?