[lld] [llvm] [RISCV] Support RISCV Atomics ABI attributes (PR #84597)

[Alex Bradbury via llvm-commits]

asb wrote:

Thanks Luke. I can reproduce locally (with GNU ld 2.42) so have gone ahead and reverted so we can decide what to do without breaking people's workflows in the meantime.

CC @kito-cheng 

It seems like there are two problems here, the first obviously by far the biggest:
* There seems to be a bug in GNU ld's elf attribute handling code that causes it to segfault when seeing an unrecognized attribute.
* Arguably warning whenever an unrecognized tag is encountered (as ld.lld does, via `ELFAttributeParser::parseAttributeList`) is overly verbose.

https://github.com/llvm/llvm-project/pull/84597