The V8 port hasn't been updated since 2013 it seems.
There have been *very* important improvements in between, including API changes and many performance and stability improvements on all platforms.
Maybe lang/v8 should be at v5.1 and lang/v8-devel at v5.5 (or at least v8-devel should be at v5.1)
Thank you very much.
The problem is the build structure, so someone needs to provide a patch
for the update.
I think, maintainers of www/chromium or devel/electron4 can help with that. Current release of v8 uses gn build system, which is also used by chromium and electron.