This requires changing our checkout strategy to check out the branch-heads branch (as documented at https://v8.dev/docs/version-numbers) instead of using the 8.4.371 branch, which never gets patches (it's always locked to 8.4.371.0).

We could also specify the v8 patch version manually, and i'm open to doing that, just wanted to do this to get it working.

Using bisect, I was able to find that the build error was introduced in
v8/v8@5bbca54,
so let's use the version before that one while we wait for upstream to
merge the patch (https://bugs.chromium.org/p/v8/issues/detail?id=10708)

Otherwise, attempts to use the i18n api (toLocaleString, Intl, etc)
raise the TypeError 'Internal error. Icu error.'

We now build against three darwin versions (Sierra, High Sierra and Catalina)
to match Ruby core. We continue to build against 3 ruby versions on Linux, but
we only deploy the ruby 2.7 builds (since they should all be identical).