Commit for ROOT6 update

[Chris Jones]

Hi,

Could I ask a committer, or anyone who is interested, to take a look at

https://trac.macports.org/ticket/45265

which is an update to the ROOT6 port.

There is one issue, which is upstream and moved to a new internal LLVM 
version, which I believe prevents building on OSX 10.6. I think this is 
hard to fix, so suspect we will just have to declare this port 
unavailable on this OS. Is this acceptable ?

cheers Chris