[lld] [lld-macho] Implement symbol string deduplication (PR #123874)

[via llvm-commits]

alx32 wrote:

Here are perf numbers for a ~100MB binary with ~400k symbols:

```
Iterations: 100
----------------------------------------------------------------------
| Command              | Avg Time (s) | Median Time (s) | Size (MB) |
----------------------------------------------------------------------
| Sym String Dedup     |     2.947943 |        2.948404 |  91.8504  |
| NO Sym String Dedup  |     2.799081 |        2.798159 | 118.1446  |
----------------------------------------------------------------------
```
So a `5.1%` slowdown for a `28.6%` size reduction.
This is on a machine with a fast SSD - the numbers might be equal on a slower I/O machine. 




https://github.com/llvm/llvm-project/pull/123874