CPATH versus -I

[Michael Dickens]

I've been working on ticket #25320 for qt4-mac, which I think is
actually an issue with 'port' itself and I've submitted ticket #25321 to
that effect.  One of the issues I've come across is: When should I be
using CPATH=<PATH:LIST> versus "-I<PATH_1> -I<PATH_2> -I..."?  Is there
any difference between them, maybe search order?  When is one preferable
to the other?  Is their interpretation compiler dependent?  Thanks in
advance! - MLD