Reland optimized-compiler-builtins config Copy of #102579 PR. From #102579: > No concerns on my side. Currently, Jyn isn't actively working on the project. I will close this PR; open another one to cherry-pick the commits, resolve conflicts, and then r+ it. > Fixes https://github.com/rust-lang/rust/issues/102560. Fixes https://github.com/rust-lang/rust/issues/101172. Helps with https://github.com/rust-lang/rust/issues/105065 (although there's some weirdness there - it's still broken when optimized-compiler-builtins is set to true). Fixes https://github.com/rust-lang/rust/issues/102560. Fixes https://github.com/rust-lang/rust/issues/101172. Helps with https://github.com/rust-lang/rust/issues/105065 r? ghost