Use protected visibility by default on ELF platforms #105518
Description
I noticed that the .so files built by x.py contain a lot of "unnecessary" PLT entries. The compiler should be using protected visibility on ELF platforms by default.
I was thinking we should be able to tie it to #[no_mangle] but on Zulip @bjorn3 proposed tying it to the SymbolExportLevel (Rust for mangled and unmangled but not exported from cdylib #[rustc_std_internal_symbol] symbols and C for #[no_mangle] symbols).