FastR update: LLVM back-end and R compatibility

The FastR team has spent most of the last year on improving the compatibility with GNU-R. This enabled FastR to run packages such as dplyr or data.table. However, these packages combine native and R code in performance sensitive code paths. Frequent transitions between native and R code incur performance hit for the FastR runtime. The solution that the FastR team has been working on is using the Graal LLVM interpreter to execute the native code inside the FastR runtime. This not only eliminates the costly transitions between native code and the FastR runtime but also allows the JIT compiler to optimize the code across this boundary. On top of that, it enables some interesting tooling opportunities such as debugging of R and C at the same time.