WT-15773 raised an issue about the use of C++20 in the default build. It turns out that we've already done this with some tests. The documentation at https://source.wiredtiger.com/develop/build-posix.html states that all you need is GCC >= 8.5 and Clang >= 7.0.1, which is no longer correct with the default build flags.

There are a few courses of action we can take:
1. Update the docs
2. Don't build anything that needs newer compilers (or C++ compilers) by default
3. Something else creative?