Created attachment 196764 [details]
Boost tends to enable more features (including new libraries) for higher standards.
Can you do exp-run on 11.2 or later with make.conf from bug 229569 comment 9? If you plan to try on -CURRENT as well better use bug 230355 as both 11.2 and 12.0 have Clang 6.0.
I saw no new failure on 11.2 with the patch applied.
A commit references this bug:
Date: Sat Sep 8 00:53:11 UTC 2018
New revision: 479222
devel/boost-all: switch to C++17 on FreeBSD >= 11.2
Exp-run by: antoine