[lld] [lld] Support RUN_LLD_MAIN_TWICE for the ELF port (PR #124441)

[Peter Smith via llvm-commits]

https://github.com/smithp35 approved this pull request.

LGTM.

Personally I quite liked the comments above the unsupported in the MachO port 
```
;; We're intentionally testing fatal errors (for malformed input files), and
;; fatal errors aren't supported for testing when main is run twice.
```
If you're in agreement, I don't have a strong opinion, perhaps worth adding
```
This test intentionally checks for fatal errors, and fatal errors aren't supported for testing when main is run twice.
```
Saves a bit of effort to look up what `main-run-twice` means, and why the test might support it.

https://github.com/llvm/llvm-project/pull/124441