remove the unstable rustdoc parameter --linker

use the code generation parameter -Clinker (same parameter as rustc)
to control what linker to use for building the rustdoc test executables.

closes: #63816

src/bootstrap/bin/rustdoc.rs

@@ -5,6 +5,7 @@
 use std::env;
 use std::process::Command;
 use std::path::PathBuf;
+use std::ffi::OsString;
 
 fn main() {
     let args = env::args_os().skip(1).collect::<Vec<_>>();
@@ -44,7 +45,9 @@ fn main() {
         cmd.arg("-Z").arg("force-unstable-if-unmarked");
     }
     if let Some(linker) = env::var_os("RUSTC_TARGET_LINKER") {
-        cmd.arg("--linker").arg(linker).arg("-Z").arg("unstable-options");
+        let mut arg = OsString::from("-Clinker=");
+        arg.push(&linker);
+        cmd.arg(arg);
     }
 
     // Bootstrap's Cargo-command builder sets this variable to the current Rust version; let's pick