Portable template jit assmbler

[melkyades]

I've been working on an interpreter for egg written in C++, because why not? I'm also planning to add template jit capabilities to it, so it'll need a codegen. I've not been able to find a portable assembler for this in C++. The idea/requirement is simple: the template jit talks to an assembler with generic registers A ... Z, and generic instructions. The assembler is instantiated for a particular arch, i.e. X64Asssembler, RISCVAssembler, etc. It maps each register to a concrete register (no regalloc needs to be done).

The question is, what's the best way to implement this. I imagine each backend having methods like this:

// X64Assembler.c
PushR()
{
    stream << bytesPushRAX
}
```

The question is how to get the bytes for each instruction with much effort.
We could hand-write each backend to emit the corresponding bytes or we could somehow write the assembly (i.e. push RAX) and pass it to an assembler (which? how?), or do something else, like generating it from ISA spec files.

I'd like it to be a separate repo so that it can be used in other projects.

[melkyades]

A few more thoughts about this, I believe we can generate C code for some archs from Smalltalk using the code we had for nativization in the powerlang repo.

One important requirement to mention is that the C lib must be free of runtime deps (i.e. the client jit should not need llvm or gcc or some assembler to be present at runtime).