Rollup merge of #132934 - Zalathar:native-libs, r=jieyouxu

Overhaul the `-l` option parser (for linking to native libs)

The current parser for `-l` options has accumulated over time, making it hard to follow. This PR tries to clean it up in several ways.

Key changes:
- This code now gets its own submodule, to slightly reduce clutter in `rustc_session::config`.
- Cleaner division between iterating over multiple `-l` options, and processing each individual one.
- Separate “split” step that breaks up the value string into `[KIND[:MODIFIERS]=]NAME[:NEW_NAME]`, but leaves parsing/validating those parts to later steps.
  - This step also gets its own (disposable) unit test, to make sure it works as expected.
- A context struct reduces the burden of parameter passing, and makes it easier to write error messages that adapt to nightly/stable compilers.
- Fewer calls to `nightly_options` helper functions, because at this point we can get the same information from `UnstableOptions` and `UnstableFeatures` (which are downstream of earlier calls to those helper functions).

There should be no overall change in compiler behaviour.

0 files changed, 0 insertions, 0 deletions