[llvm] [Object] Beginnings of SFrame parser and dumper (PR #147294)

[Pavel Labath via llvm-commits]

https://github.com/labath commented:

> Is there a specification that can be pointed to in the commit description? It's a bit hard to review a parser without actually knowing what the specification is :)

Sorry about that. The specification is [here](https://sourceware.org/binutils/wiki/sframe) and this is the [RFC thread](https://discourse.llvm.org/t/rfc-adding-sframe-support-to-llvm/86900). It's linked to in the first PR, but I'm going to add it to the next couple of PRs at least.

The SFrame section starts with a preamble, which contains which contains the version number, and it is the only fixed part of the format. It is followed by the header, whose layout can depend on the version (but we're only supporting the current version (2)). The sframe sections are *not* linked by concatenating, so the section always contains only one header/preamble pair.

https://github.com/llvm/llvm-project/pull/147294