This JIT is tightly coupled to the ASTInterpreter, at every CFGBlock* entry/exit
on can switch between interpreting and directly executing the generated code without having
to do any translations.
Generating the code is pretty fast compared to the LLVM tier but the generated code is not as fast
as code generated by the higher LLVM tiers.
But because the JITed can use runtime ICs, avoids a lot of interpretation overhead and
stores CFGBlock locals sysbols inside register/stack slots, it's much faster than the interpreter.