Avoid adding builtin functions to `symbols.o` We found performance regressions in #113923. The problem seems to be that `--gc-sections` does not remove these symbols. I tested that lld removes these symbols, but ld and gold do not. I found that `used` adds symbols to `symbols.o` at https://github.com/rust-lang/rust/blob/3e202ead604be31f4c1a5798a296953d3159da7e/compiler/rustc_codegen_ssa/src/back/linker.rs#L1786-L1791. The PR removes builtin functions. Note that under LTO, ld still preserves these symbols. (lld will still remove them.) The first commit also fixes #118559. But I think the second commit also makes sense.