[clang][NFC] sort C standards on status page in reverse chronological order (#102844)

Put the newest standards first, same as for the [C++ status
page](https://clang.llvm.org/cxx_status.html).

The diff is pretty busted, but I swear I copy & pasted faithfully 😅 

The only change beyond shuffling sections around is unfolding the
sections for C99/C11 (6dbce28), which
isn't necessary anymore now that they're safely tucked away towards the
end of the page.

Author: h-vetinari