Using <filesystem> on macOS 10.13 with clang++-mp-13

[Ken Cunningham]

> On Jul 13, 2022, at 2:33 PM, Ryan Schmidt <ryandesign at macports.org> wrote:
> 
> On Jul 3, 2022, at 13:38, Ken Cunningham wrote:
> 
>> You can (sometimes) use macports-libcxx to get past this. This however introduces two versions of libc++.dylib into the softare mixture, and this sometimes causes errors due to incompatibilities between libc++ versions (ODR errors). If you are taking this route, linking in the newer libc++.a statically has a higher chance of working properly (that is what Chrome does on older MacOS systems).
> 
> If a port X links to a static library provided by a port Y, you should increase the revision of port X whenever port Y is updated to a new version so that your port X receives the new version of the static library. A comment should be left in port Y advising whoever updates it to do that.
> 
> 

If anyone is ever motivated to update macports-libcxx beyond libcxx-11 it would be best to be very careful.

ODR errors due to divergence from older libcxx versions are thought to increase as of llvm/libcxx-12, so lots of testing might be needed.

This whole plan is obviously very fragile.

K