I have from time to time seen messages like the following when updating things on my FreeBSD systems
pid 85886 (conftest), uid 0: exited on signal 11 (core dumped)
Since they were pretty sporadic and nothing else was acting up it generally went uninvestigated.
Then a little time ago I updated a load of ports on my web host and the messages just became eerily frequent so I decided to dig into it a bit.
Looking through logs and compile output revealed nothing wrong.
Google to the rescue! I found out that this is actually GNU autoconf forcing this behaviour to make sure the system deals with a segfault correctly.
FreeBSD-questions@ cleared this up years ago, so I guess I should have checked at once and saved myself some worry..