The autoconf checks if the build environment has a sane C compiler, standard C library, shell and command and all. At that time, well 30 years ago, it might be useful, but today, it's completely garbage. If the build environment found out to have an insane non standard conforming behaviours, there is nothing to do about it. And the autoconf's workaround implementation almost always won't work today in such an insane environment anyway.

What I don't get is the autoconf failed to update it to the modern situation and still keeping the behaviour that is totally irrelevant and considered harmful today.