seeing a build problem on the default branch when building on macOS (10.15.6) using Homebrew for dependencies and Apple’s clang version 12.0.0 (clang-118.104.22.168).
does it work if you try building with CXXFLAGS="-std=c++14 "?
Your suggestion worked for me.
So, if it is now accepted to require a C++14 compatible compiler we should just document that and change the current configure test which looks for C++11 to look for C++14 instead.
Otherwise, the use of "auto" for parameters should be abandoned. I'm not following in detail the discussion on this between jwe and Rik but it seems they are planning some way to work around this ...