From: Tim Hunter <cyclists@...>
Date: 2002-11-27T09:28:45+09:00
Subject: extconf.rb & gcc 3.2

I'm building a Ruby 1.6.7 extension using extconf.rb and gcc 3.2, the default
compiler for Mandrake 9.0.

I notice that extconf.rb automatically adds -I/usr/local/include to the
list of gcc switches. This causes gcc to complain:

cc1: warning: changing search order for system directory "/usr/local/include"
cc1: warning:   as it has already been specified as a non-system directory

If I read the gcc man page correctly, gcc thinks that /usr/local/include
is a "standard system directory" and should not appear on an -I switch:

   "It is dangerous to specify a standard system include directory in an
    -I option.  This defeats the special treatment of system headers.
    It can also defeat the repairs to buggy system headers which GCC
    makes when it is installed."

I did a quick Google for this message text and learned that apparently it
was added after 2.95 and has taken many people by surprise. 

Does mkmf.rb need to be updated to handle gcc 3.2? Is there a way to tell
mkmf.rb to NOT add the -I/usr/local/include switch?