[lld] [ELF] PHDRS update while condition and phdrs.s unclose2.lds output (PR #100918)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Using `till(";")` for the inner loop would cause inferior diagnostics for the following case:

```
ld.lld: error: 1.lds:1: unexpected header attribute: }
>>> PHDRS {all PT_LOAD FILEHDR PHDRS }
>>> 
```

https://github.com/llvm/llvm-project/pull/100918