Unfortunately, XCode 9 is introducing changes to the standard library that are incompatible with that version of ROOT. There is a small chance that reconfigure and rebuild ROOT itself from scratch will solve the problem (depending on which plugin you need).
If this does not work, you will need to use the master branch of ROOT with commit 263508429dec26449513914e71f0f71c9ce9485f or later.
Cheers,
Philippe.