`rustdoc` rejects (instead of ignoring) some unneeded `rustc` command-line flags like `-l...`

Context

IIUC rustdoc needs to be invoked with the same command-like flags as rustc (similarly to clippy-driver) - this ensures that rustdoc sees the code in the same way as rustc does. For example:

• the same --cfg flags should be used to include the same conditional code,
• the same -L flags should be used so rustdoc can discover other crates that the current crate depends on

And it seems that rustdoc happily accepts most of the same flags as rustc, even ones that are not really needed for generating documentation - for example:

• -Clink-arg=..., -Clto=no, -Copt-level=3 and other codegen flags
• -Zdep-info-omit-d-target and other unstable flags
• --cfg and -L flags mentioned above

Accepting the same flags as rustc is very desirable, because this helps build systems (e.g. gn used by Chromium, but probably also Bazel, Buck, etc.) to pass more-or-less the same command-line flags to rustdoc as the ones that are passed to rustc.

Problem

Repro steps:

$ which rustdoc
/usr/local/google/home/lukasza/.cargo/bin/rustdoc

$ rustdoc --version
rustdoc 1.96.0-nightly (80381278a 2026-03-01)

$ cat repro.rs
/// Documentation of `foo`.
pub fn foo() {
    todo!()
}

$ rustdoc repro.rs  # Works fine

$ rustdoc repro.rs -lglib-2.0  # PROBLEM: errors out
error: Unrecognized option: 'l'

Expected behavior: rustdoc accepts and ignores linking flags like -lglib-2.0

Actual behavior: rustdoc rejects -lglib-2.0 command-line flag

Start by reproducing the rustdoc repro.rs command with -lglib-2.0 and compare rustdoc's argument handling with rustc and clippy-driver. Trace the rustdoc command-line entry point to determine how linking flags are classified; done means rustdoc accepts and ignores -l flags while preserving existing behavior, with a regression test for the reported command.