Add support for LLVM-style syntax

[kfl]

LLVM has chosen an unconventional syntax for their eBPF assembly syntax. And this style is also used for output by, for instance, bpftool. Thus it makes sense to support this syntax both as input and output.

[madsobitsoe]

Do you happen to know where a specification of the LLVM-style syntax can be found?
I fail to find one with my search-skills.

[kfl]

The problems with eBPF syntax are:

• There are so many to chose from.
• None of them are fully specified/documented (including the one used by ebpf-tools)

[kfl]

Tongue in cheek, I think the best documentation is https://llvm.org/doxygen/BPFAsmParser_8cpp_source.html, because it doesn't look like llvm-mc has any documentation regarding its input format.

[madsobitsoe]

Wonderful!
I will let you know if I ever get started.