Auto merge of #13212 - Brooooooklyn:master, r=epage

Add cargo:rustc-cdylib-link-arg into RESERVED_PREFIXES list

After #12201 was merged, the `cargo:rustc-cdylib-link-arg` in build script no longer works
```rs
println!("cargo:rustc-cdylib-link-arg=-Wl");
println!("cargo:rustc-cdylib-link-arg=-undefined");
println!("cargo:rustc-cdylib-link-arg=dynamic_lookup");
```

Author: bors

Diff for: src/cargo/core/compiler/custom_build.rs

@@ -707,6 +707,7 @@ impl BuildOutput {
             "rustc-link-lib=",
             "rustc-link-search=",
             "rustc-link-arg-cdylib=",
+            "rustc-cdylib-link-arg=",
             "rustc-link-arg-bins=",
             "rustc-link-arg-bin=",
             "rustc-link-arg-tests=",