[ELF] Speculatively fix older MSVC after &ctx change
https://lab.llvm.org/buildbot/#/builders/107/builds/3155
```
error C2039: 'ctx': is not a member of '`anonymous-namespace'::Writer<ELFT>::fixSectionAlignments::<lambda_38c4af40b02773e966aeff2e6bd45bf2>'
```
