Message 297847 - Python tracker
Yea I'm building Python 3.6.1 from source, using gcc and --with-cxx-main=correct/location/to/g++ flag. So the warning message appears during ./configure about that it can't find g++. I didn't try to patch it using the attachments of this issue. Since I was hoping it's fixed in the release itself. I was using gcc/g++ version 4.9.