Note that this "fix" doesn't actually change anything, as it results in gcc being invoked with `-std=c++17 -std=c++11`, and the latter option prevails. Building with libxml2-dev 2.12.7+dfsg+really2.9.14-0.3 still fails.
The reason why the salsa build succeeded nonetheless is thanks to 2.12.7+dfsg+really2.9.14-0.4 having just been released today and no longer pulling in ICU (#1092484), thus solving the issue.
