This patch contains the SIE-specific parts of the unified LTO pipeline. See this conversation: https://discourse.llvm.org/t/rfc-a-unified-lto-bitcode-frontend/61774/15
If a vendor wants to change some driver default, that's fine, especially when on/off already has a condition. But please include full context per https://llvm.org/docs/Phabricator.html#requesting-a-review-via-the-web-interface and add a clang/test/Driver/ test.
Also, "SIE" isn't a clear abbreviation. PS4 seems more understandable by other contributors.