use Config::get_builder_toml for ci-rustc config parsing

Signed-off-by: onur-ozkan <work@onurozkan.dev>

src/bootstrap/src/core/config/config.rs

@@ -2346,18 +2346,15 @@ impl Config {
                     self.download_ci_rustc(commit);
 
                     if let Some(config_path) = &self.config {
-                        let builder_config_path =
-                            self.out.join(self.build.triple).join("ci-rustc").join(BUILDER_CONFIG_FILENAME);
-
-                        let ci_config_toml = match Self::get_toml(&builder_config_path) {
+                        let ci_config_toml = match self.get_builder_toml("ci-rustc") {
                             Ok(ci_config_toml) => ci_config_toml,
                             Err(e) if e.to_string().contains("unknown field") => {
                                 println!("WARNING: CI rustc has some fields that are no longer supported in bootstrap; download-rustc will be disabled.");
                                 println!("HELP: Consider rebasing to a newer commit if available.");
                                 return None;
                             },
                             Err(e) => {
-                                eprintln!("ERROR: Failed to parse CI rustc config at '{}': {e}", builder_config_path.display());
+                                eprintln!("ERROR: Failed to parse CI rustc config.toml: {e}");
                                 exit!(2);
                             },
                         };