From LibreSSL versions 3.2.1 through 3.4.0, our configure script would conclude that TLSv1.3 as supported, but it actually wasn't. This led to annoying breakage like #40128 (closed) and #40445 (closed).
Now we give an error message if we try to build with one of those versions.
Closes #40511 (closed).
Note that this MR is built on top of !486 (merged), since it touches the same part of the configure.ac file, and I wanted to avoid a conflict.
When I was writing this patch, I considered having this error only happen at runtime if we were running as a relay, or making it possible to disable this message with
--disable-module-relay. (The errors above only happen when running as a relay.) I decided not to take that route, since we should just encourage everybody to have a crypto library that works with Tor.