Rollup merge of #70868 - petrochenkov:linkorder, r=nagisa,mati865

rustc_codegen_ssa: Refactor construction of linker arguments

And add comments.

This PR doesn't reorder any linker arguments and therefore shouldn't contain any observable changes.

The next goal here is to
- Factor out order-independent linker arguments in the compiler code and in target specifications and pass them together. Such arguments generally apply to the whole linking session or the produced linking result rather to individual object files or libraries.
- Figure out where exactly among the remaining order-dependent arguments we should place customization points like `-C link-args` and `-Z pre-link-args`.
- Possibly provide command line opt-outs for options that are currently passed unconditionally (like CRT objects or arguments defined by the target spec).
- Document and stabilize the customization points that are not yet stable (#70505).