chore(changelog): add fragment for #8095

Author: Ralph Küpper

changelog.d/8095-elf-object-source-identity.md

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+`cargo-test` is green again on Linux. Four `perry-codegen` tests
+(`rs4gc_canonicalizes_construction_time_folds_before_root_liveness` and the
+three `native_emit` construction-path tests) assert that textual and native
+construction emit byte-identical output. The generated code had already
+converged; the objects differed only in the name LLVM records for the module.
+
+Nothing set `source_filename`, so LLVM fell back to whatever path reached the
+assembler: the textual pipeline writes each module to a per-call temp file, so
+its recorded name carried a random nonce (`perry_llvm_<nonce>.ll`), while
+native construction recorded its in-memory module id (`perry_native_module`).
+ELF stores that name as an `STT_FILE` symbol, so the two paths could never
+agree and neither was reproducible run to run. Mach-O records no such symbol,
+which is why all four passed on a macOS host and failed only on the Linux
+runner.
+
+All three module-header sites (`to_ir`, `skeleton_ir`, and the per-codegen-unit
+prologue) now emit an explicit `source_filename`, so the recorded name is the
+same constant on both paths and independent of the temp path. Emitted objects
+no longer embed a random temp filename, so they are reproducible across runs.
+
+The three `native_emit` tests only ever ran against the host triple, so on a
+macOS machine they exercised Mach-O exclusively — the one object format that
+does not record this name. `native_and_text_arms_agree_on_an_elf_target` now
+pins the comparison to `x86_64-unknown-linux-gnu` and asserts the bytes start
+with `\x7fELF` before comparing, so it cannot pass by testing the wrong format;
+it is sabotage-tested against the un-fixed emission.