refactor: move lld-rs to seperate repository

[baszalmstra]

Move LLD to its own repository so we (but mostly other folks) can progress its version regardless of the main Mun repository.

The new location for the renamed library (lld-rs instead of mun-lld) can be found here: https://github.com/mun-lang/lld-rs

Fixes: #353

[baszalmstra]

Im just double checking that mun still builds when using the external repository before I publish lld-rs.

@ghaith I created a new repository from the mun repository where I rewrote most of history. I credited you in a few of the commits with improvements you made. I hope that's ok?

[ghaith]

Yes sounds good to me. Thanks.

[codecov]

Codecov Report

Merging #373 (ebca466) into main (cdfda48) will increase coverage by 0.07%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##             main     #373      +/-   ##
==========================================
+ Coverage   82.54%   82.61%   +0.07%     
==========================================
  Files         264      262       -2     
  Lines       15248    15219      -29     
==========================================
- Hits        12586    12573      -13     
+ Misses       2662     2646      -16     

Impacted Files	Coverage Δ
crates/mun_codegen/src/linker.rs	25.33% <33.33%> (ø)

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