Discern ELF targeting eBPF for Windows from ones targeting Linux

Nobody has claimed this yet.

### Describe the feature you'd like supported

Right now it is not possible to determine the target platform from the contents of an ELF. A program compiled against Linux headers looks the same as a programs compiled against Windows ones. This is a problem for projects which need to support loading ELF from both platforms because while the ELF are superficially similar the contents aren't compatible:

* Constants like map type differ
* Section names are distinct
* Even where section names match, programs are not necessary compatible (see https://github.com/microsoft/ebpf-for-windows/issues/3212)

There should be a way for toolchains to figure out the platform of an ELF.

### Proposed solution

1. Add a new ELF section similar to `.license` which contains a string that indicates the platform, e.g. `windows` or `linux`.
2. Somehow set the ELF OS/ABI field to something meaningful.
```
$ readelf -h testdata/loader-clang-el.elf
ELF Header:
Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class: ELF64
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
```

It would be best if this was coordinated with upstream libbpf somehow.

### Additional context

_No response_