building from source with libc++

[Ken Cunningham]

> 
> Newer systems will stumble on these ports as by default clang will add -stdlib=libstdc++ and that doesn't work with cxx11; you get link errors.
> 
> 

One typo, sorry -- this should say "Older systems will stumble on these ports ...", not "Newer systems will stumble on these ports ."

my apologies for letting this typo slip through on a detailed post.

Ken