[lld] [lld] Support thumb PLTs (PR #86223)

[via llvm-commits]

PiJoules wrote:

> This Thumb PLT support is for very restricted use cases. The lack of a MMU implies no sharing for the text segment used by two processes:
> 
> * Two processes running the same executable must have different data segments. The System V dynamic linking model requires a constant distance between the text segment and the data segment. Corollary: the text segment cannot be shared.
> * Similarly, a shared object's text segment cannot be shared by two processes running different executables.
> 
> Perhaps the use case has a stronger requirement: no two executables (nanoapps?) are running at the same time.
> 
> It seems useful to update the description to clarify the case. The code generally looks good.

Updated

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