elf: add PT_RISCV_ATTRIBUTES program header

Attribute is ignored for now.

It is supposed to check ABI compatiblity and reject loading incompatible images.
Haiku currently do not use multiple ABIs for RISC-V so it is safe to ignore attributes.

PT_RISCV_ATTRIBUTES program header is produced by default in GCC 13 and Clang 17.

Change-Id: I4659e9bacbf34a2a0bc16b34c2aaa37232d700fa
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6948
Reviewed-by: David Karoly <karolyd577@gmail.com>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>

elf.h: add some missing defines

Needed for ghc.

elf2aout: import from FreeBSD

The sparc openboot implementation can run executables in the a.out
format. We used to generate these using objcopy, but this does not work
anymore as binutils is deprecating a.out format support.

- Import elf2aout from FreeBSD
- Add some missing bits to our elf.h and have a copy of it in the build
headers so it can be used to build elf2aout for the host platform
(tested for Linux)
- Use it to generate the sparc haiku_loader
- Adjust the bootloader linker script to have two "program headers": one
that is not loadable and contains the ELF headers, and the second one
that is loadable and contains the actual code and data. Unlike
objcopy, elf2aout relies only on the program headers to know what to
put in its output file (sections are ignored), so this is required
otherwise we end up with the ELF header nested inside the a.out file,
and everything offset from the expected load address as a result.

Confirmed that this allows to build the loader and run it as far as
before, so I'm back to needing to implement some MMU support now.

FreeBSD commit: 7551d83c353e040b32c6ac205e577dbc5f2c8955

Change-Id: I90b48e578fa7f148aeddd8c5998fdddc5cfa73fa
Reviewed-on: https://review.haiku-os.org/c/1557
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>