Add V8 testing on CI

[kripken]

This adds v8 from jsvu to CI, and a single lit test that uses it.

Later PRs will use d8 to test more complex things (in particular,
things like JSPI that need a recent d8, and not older node).

[kripken]

Apparently jsvu is not compatible with alpine - the binaries it provides are not compatible with that linux distro/arch. I think I just need to skip the test there.

@tlively I can't figure out how to do that. The llvm docs for lit do mention --xfail and the env var LIT_XFAIL, but the lit we use, installed by python, does not actually support --xfail, and it seems to ignore the env var as well. I guess it is a limited version of the real one? (In llvm-lit I do see --xfail exists.)

Is there some other way to skip tests in lit? It seems like we might never have done so before in binaryen?

[kripken]

I found no better workaround for skipping these tests on alpine than to just delete them. If we can find a better workaround, we can apply that later.

[tlively]

The lit we use should be a repacked version of the original llvm lit, so I would have expected it to support all the same features. (Our filecheck is a simplified Python port of the original filecheck, though.)

I can try to investigate xfail next week. You’re right that it’s not something we’ve had to use yet in Binaryen.