openfortivpn | Client for PPP+SSL VPN tunnel services | VPN library

For the first question I looked into the configure file itself. It was a shell script so I could just replace append -x to #! /bin/sh at the very top to make shell echo every command it ran.

That turned out to be unmaneagable since configure was huge and there was a lot of jumping between functions. So I wondered what was that magical configure script and what was that ./autogen.sh script that I ran earlier and how could I make it run in a more verbose manner. Turns out that autogen is a description that's read by autoconf and the result is written as a configure file. Turn's out there's a documentation page explaining how to debug the resulting script.

As instructed I have wrapped the call that checked for arpa/inet.h in the configure script with set -x and set +x.

I couldn't find any find or anything similar in it but I saw some gcc -E test.c here and there. I guessed that autoconf was creating a simple C file that contained an #include directive and then autoconf parsed the output of gcc to tell if the header could be found at all.

So my next test was to create a simple test file that did exactly that: