Adding the notion of <ANY> for declared but not assigned values.

[titomeister]

In the GCC2CAST pipeline, any declared variables that aren't assigned a value like
int x;
Currently have their default values set to -1. We would like to change that so that it's an value of sorts. This way it's more clear that it's an actual declaration but not an assignment.
This is more likely going to be done at the CAST level by leveraging the LiteralValue node.