[llvm] [NFC][MC][Dwarf] Add Range/Location List Entry fragment to reduce memory usage (PR #146098)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> ...
> @aengelke has shared some ideas for improvement in this area but hasn’t had time to integrate them into LLVM. I’d prefer we explore [general fragment content](https://maskray.me/blog/2024-06-30-integrated-assembler-improvements-in-llvm-19) optimizations before introducing complex code like this. While I believe a custom fragment could offer greater efficiency than a generic fragment improvement, the latter might be sufficient to reduce the need for introducing a new fragment.
> 
> Your debug info improvements are valuable, but do they truly require such intricate assembler changes?
> 
> To make `MCLEBFragment` smaller, we can remove the `Fixups` member variable and move `IsSigned` to MCFragment.

Uploaded https://github.com/llvm/llvm-project/pull/146307 , which should make a new fragment less necessary.

https://github.com/llvm/llvm-project/pull/146098