Rollup merge of #122723 - bjorn3:archive_writer_fixes, r=nnethercote

Use same file permissions for ar_archive_writer as the LLVM archive writer

This is required to switch to ar_archive_writer in the future without regressions. In addition to this PR support for reading thin archives needs to be added (rust-lang/rust#107407) to fix all known regressions.

Fixes rust-lang/rust#107495

Author: matthiaskrgr