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

[Fangrui Song via llvm-commits]

MaskRay wrote:

Thanks for the suggestion.
I was lazy with my sed command. To add the comment, I have switched to:

```
comment="This test intentionally checks for fatal errors, and fatal errors aren't supported for testing when main is run twice."
xargs </tmp/0 sed -Ei "1s/(;|#|\/\/) REQUIRES: .*/\0\n\1 "$comment"\n\1 XFAIL: main-run-twice/;t;1s/^/# "$comment"\n# XFAIL: main-run-twice\n/"
```

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