- Building QtWebEngine fails with error "Update aspirational_scripts per Unicode 9.0"
- Install ICU 58 or late on Linux host
- Build QtWebEngine with system_icu option
- Build succeeds.
It is due to ICU 58 has been out with the release of Unicode 9.0.
Upstream chromium has already been fixed 
On qtwebengine-chromium, older than 56-based branches are affected by this issue.