`cargo::rustc-link-arg-cdylib` should not be rejected if `cdylib` is not in `crate-type`

[usamoi]

Problem

Consider this package.

Cargo.toml:

[package]
name = "foo"
version = "0.0.0"
edition = "2024"

build.rs:

fn main() {
    println!("cargo::rustc-link-arg-cdylib=-lhack");
}

Cargo emits a warning for it.

warning: foo@0.0.0: cargo::rustc-link-arg-cdylib was specified in the build script of foo v0.0.0, but that package does not contain a cdylib target

Allowing this was an unintended change in the 1.50 release, and may become an error in the future. For more information, see <https://github.com/rust-lang/cargo/issues/9562>.

This warning may seem reasonable; however, users may take advantage of it by using

cargo rustc --crate-type cdylib

And it totally works. In this case, there should be no warning. The warning is configured only to inform the user not to rely on rustc-link-arg-cdylib being transitive through dependencies. Therefore, we should remove this warning, or at least stop telling the user that it will be rejected.

cc #9562

Steps

No response

Possible Solution(s)

No response

Notes

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Version