6502: Introduce inline assembly labels and relative addressing

[Miezekatze64]

This allows to use and define labels in 6502 assembly (also allows to acess extrn functions) and adds syntax for relative addresses used in branch instructions

Examples:

__asm__("label:",
"BCC label",
"BMI *+42")

[rexim]

I think it's a bit sus that something like this doesn't error out

main() {
    __asm__("label:", "label:");
}

What's expected in here?

[Miezekatze64]

Fixed it now, this also adds the name_loc fields to ir::Global

[rexim]

@Miezekatze64 alright, looks good! Thank you!