Auto merge of #83593 - petrochenkov:nounwrap, r=nagisa

rustc_target: Avoid unwraps when adding linker flags

These `unwrap`s assume that some linker flags were already added by `*_base::opts()` methods, but that's doesn't necessarily remain the case when we are reducing the number of flags hardcoded in targets, as https://github.com/rust-lang/rust/pull/83587 shows.

r? `@nagisa`