Now homebrew upgrades ROOT6 to 6.10/06. This version solves my problem! Just do
brew upgrade root6
I confirm that upgrading root and downgrading XCode solves the original problem. Nevertheless I still have the second problem:
francescolosterzo MCStudies$ python makePlots.py
fatal error: file
'/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/memory'
modified since it was first processed
I am trying to avoid to rebuild ROOT from scratch, but if it’s the only solution I’ll go for it.