Unrolled build for rust-lang#126616

Rollup merge of rust-lang#126616 - onur-ozkan:less-warnings, r=Mark-Simulacrum

less bootstrap warnings

This is how the build logs looks like currently:

```sh
$ x build
Building bootstrap
   Compiling bootstrap v0.0.0 (/home/nimda/devspace/onur-ozkan/rust/src/bootstrap)
    Finished `dev` profile [unoptimized] target(s) in 3.43s
WARNING: no codegen-backends config matched the requested path to build a codegen backend. HELP: add backend to codegen-backends in config.toml.
WARNING: creating symbolic link `/home/nimda/devspace/.other/rustc-builds/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/rustc-src/rust` to `/home/nimda/devspace/onur-ozkan/rust` failed with File exists (os
error 17)
Creating a sysroot for stage2 compiler (use `rustup toolchain link 'name' build/host/stage2`)
WARNING: creating symbolic link `/home/nimda/devspace/.other/rustc-builds/build/x86_64-unknown-linux-gnu/ci-rustc-sysroot/lib/rustlib/rustc-src/rust` to `/home/nimda/devspace/onur-ozkan/rust` failed with File e
xists (os error 17)
Building tool rustdoc (stage1 -> stage2, x86_64-unknown-linux-gnu)
   Compiling rustdoc v0.0.0 (/home/nimda/devspace/onur-ozkan/rust/src/librustdoc)
   Compiling rustdoc-tool v0.0.0 (/home/nimda/devspace/onur-ozkan/rust/src/tools/rustdoc)
    Finished `release` profile [optimized + debuginfo] target(s) in 13.57s
Build completed successfully in 0:00:17
```

This PR removes artifact linking warnings and only shows the codegen-backend warning if explicitly called or during Dist or Install steps.

src/bootstrap/src/core/build_steps/compile.rs

@@ -1290,15 +1290,21 @@ fn needs_codegen_config(run: &RunConfig<'_>) -> bool {
 pub(crate) const CODEGEN_BACKEND_PREFIX: &str = "rustc_codegen_";
 
 fn is_codegen_cfg_needed(path: &TaskPath, run: &RunConfig<'_>) -> bool {
-    if path.path.to_str().unwrap().contains(CODEGEN_BACKEND_PREFIX) {
+    let path = path.path.to_str().unwrap();
+
+    let is_explicitly_called = |p| -> bool { run.builder.paths.contains(p) };
+    let should_enforce = run.builder.kind == Kind::Dist || run.builder.kind == Kind::Install;
+
+    if path.contains(CODEGEN_BACKEND_PREFIX) {
         let mut needs_codegen_backend_config = true;
         for backend in run.builder.config.codegen_backends(run.target) {
-            if path.path.to_str().unwrap().ends_with(&(CODEGEN_BACKEND_PREFIX.to_owned() + backend))
-            {
+            if path.ends_with(&(CODEGEN_BACKEND_PREFIX.to_owned() + backend)) {
                 needs_codegen_backend_config = false;
             }
         }
-        if needs_codegen_backend_config {
+        if (is_explicitly_called(&PathBuf::from(path)) || should_enforce)
+            && needs_codegen_backend_config
+        {
             run.builder.info(
                 "WARNING: no codegen-backends config matched the requested path to build a codegen backend. \
                 HELP: add backend to codegen-backends in config.toml.",

src/bootstrap/src/utils/helpers.rs

@@ -135,7 +135,7 @@ pub fn symlink_dir(config: &Config, original: &Path, link: &Path) -> io::Result<
     if config.dry_run() {
         return Ok(());
     }
-    let _ = fs::remove_dir(link);
+    let _ = fs::remove_dir_all(link);
     return symlink_dir_inner(original, link);
 
     #[cfg(not(windows))]