Support Truffle objects in globals

[chrisseaton]

No description provided.

[chrisseaton]

This works for Ruby code storing managed Ruby objects in global variables.

[chrisseaton]

This is ready for initial review. Ignore the JRuby test failure for now.

Key comment:

https://github.com/graalvm/sulong/pull/340/files#diff-a39e5fc5437b3cb9251c567960163ba6R36

Problem I need to solve:

https://github.com/graalvm/sulong/pull/340/files#diff-ace6de25373f780bf4543873d50a681fR1051

[ghost]

This will be useful for the 30 odd global variables in the R FFI, which I have been ignoring so far (or mapping to functions assuming they are read-only)

[mrigger]

I'm not sure if it is a good idea to have isUninitialized, isInitialized, isNative and isManaged in the LLVMNode class, since the methods are not really related to it. I think one of the two options would work better:

1. Directly call the guard, which would create a direct correspondence between the guard (e.g., globalVariableStorage.isInitialized) and initialize method (e.g., globalVariableStorage.initialize).
2. Make a helper class for it, if you think that it is likely that we will replace the guard test in the future.

[chrisseaton]

Fixed by putting them in a separate file and using @ImportStatic.

[mrigger]

Looks good! I noted a few things in inline comments.