1.80.0 issue with Clang 15

From: Peter Dimov (pdimov_at_[hidden])
Date: 2022-09-10 10:30:41

I'm getting multiple reports that ContainerHash 1.80.0 doesn't
compile with Clang 15, due to the following change to Config
unfortunately not being part of the 1.80.0 release:

https://github.com/boostorg/config/commit/f0af4a9184457939b89110795ae2d293582c5f66

Since the plans for 1.80.1 have been abandoned, it's not clear
what we can do about that except probably updating the
Known Issues section.