GC bug: Args values are getting collected prematurely

[seven1m]

I discovered this during my work on #2274, with the builds of clang and gcc provided by nix.

Specifically this test:

spec/core/io/write_spec.rb gets this error: Errno::ENOENT

But the error message is a red herring. The actual issue is that File.open gets its path argument collected and overwritten with a different (nonsensical) string value.

Args has a Vector<Value>, which in turn has a pointer to the (non-GC-managed) heap. The GC doesn't know to follow the Vector and doesn't see the Values inside it as reachable.

There is some discussion in Discord: https://discord.com/channels/868454594085281793/1307889414457790464