Replace uBPF with LLVM

[Alan-Jowett]

@alessandrogario suggested an interesting idea to research during the triage meeting on 5/2/2022.

His suggestion is that we could replace uBPF with LLVM for the generation of machine code during JIT.

Here is my suggestion for how this could be done:

1. Use the bpf_code_generator from the bpf2c tool to parse the ELF file and generate a "raw" C file (with neither driver nor dll skeleton code).
2. Parse the generated C code using the LLVM / Clang front end.
3. Pass the resulting IR to https://www.llvm.org/docs/CodeGenerator.html

[Alan-Jowett]

See: LLVMTargetMachineEmitToMemoryBuffer as a starting point for emitting machine code.