[lld] [WIP][lld] Support thumb PLTs for cortex-M (PR #86223)

[Peter Smith via llvm-commits]

https://github.com/smithp35 commented:

I know this is marked WIP so please ignore my comments if you don't want them.

For Cortex-m PLTs presumably for shared-libraries? Aren't a great fit due to the lack of an MMU. Although much more work to implement the fdpic ABI https://github.com/mickael-guene/fdpic_doc/blob/master/abi.txt may be a better fit. 

https://github.com/llvm/llvm-project/pull/86223