Auto merge of #140872 - bjorn3:elf_use_used_linker, r=nikic

Make #[used(linker)] the default on ELF too

`#[used]` currently is an alias for `#[used(linker)]` on all platforms except ELF based ones where it is an alias for `#[used(compiler)]`. The latter has surprising behavior and the LLVM LangRef explicitly states that it "should only be used in rare circumstances, and should not be exposed to source languages." [^2]

The reason `#[used]` still was an alias to `#[used(compiler)]` on ELF is because the gold linker has issues with it. Luckily gold has been deprecated with GCC 15 [^1] and seems to be unable to bootstrap rustc anyway [^3]. As such we shouldn't really care about supporting gold.

This would also allow re-enabling start-stop-gc with lld.

cc rust-lang/rust#93798
Likely fixes rust-lang/rust#85045

[^1]: https://lists.gnu.org/archive/html/info-gnu/2025-02/msg00001.html
[^2]: https://llvm.org/docs/LangRef.html#the-llvm-compiler-used-global-variable
[^3]: rust-lang/rust#139425

Author: bors