deps: update V8 to 5.6
Depends on https://github.com/nodejs/node/pull/9618.
V8 5.6 should become stable next week. It stable now!
I'm opening the PR now to track eventual issues with CI.
CI: https://ci.nodejs.org/job/node-test-commit/7473/?auto_refresh=true
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
commit message follows commit guidelines
Affected core subsystem(s)
v8