Don't set CPLUS_INCLUDE_PATH?
I am now doing that. :)
Seriously, I'm not sure why you set that variable. I never heard of it before, and usually the safest way to get includes added to the compiler flags is via CXXFLAGS and CFLAGS.
Long ago in a galaxy far away, when I first joined the project, I noticed the variable being set in the /etc/profile.d/qt.sh script that came with the Slackware qt3 package. I presumed the variable was important. Of course, that script is for run time and not for compiling. Over time I have been learning to strip many environment variables from within my build environment, but that one slipped through unnoticed until this mess surfaced.
Maybe we should have a short snippet in our wiki with what are appropriate environment variables, which ones to avoid, and what is appropriate for CXX/CFLAGS?
Good idea! At least make mention of this problematic variable, as it took quite a while (and a couple of bug reports) for both of us to even begin to figure out what was going on. ;-)
Tim