implement new x flag: --skip-std-check-if-no-download-rustc

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

src/bootstrap/src/core/build_steps/check.rs

@@ -60,6 +60,13 @@ impl Step for Std {
     }
 
     fn run(self, builder: &Builder<'_>) {
+        if !builder.download_rustc() && builder.config.skip_std_check_if_no_download_rustc {
+            eprintln!(
+                "WARNING: `--skip-std-check-if-no-download-rustc` flag was passed and `rust.download-rustc` is not available. Skipping."
+            );
+            return;
+        }
+
         builder.require_submodule("library/stdarch", None);
 
         let target = self.target;

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

@@ -423,6 +423,9 @@ pub struct Config {
 
     /// Cache for determining path modifications
     pub path_modification_cache: Arc<Mutex<HashMap<Vec<&'static str>, PathFreshness>>>,
+
+    /// Skip checking std if `rust.download-rustc` isn't available.
+    pub skip_std_check_if_no_download_rustc: bool,
 }
 
 #[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
@@ -1507,6 +1510,7 @@ impl Config {
         config.enable_bolt_settings = flags.enable_bolt_settings;
         config.bypass_bootstrap_lock = flags.bypass_bootstrap_lock;
         config.is_running_on_ci = flags.ci.unwrap_or(CiEnv::is_ci());
+        config.skip_std_check_if_no_download_rustc = flags.skip_std_check_if_no_download_rustc;
 
         // Infer the rest of the configuration.
 

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

@@ -182,6 +182,9 @@ pub struct Flags {
     /// Make bootstrap to behave as it's running on the CI environment or not.
     #[arg(global = true, long, value_name = "bool")]
     pub ci: Option<bool>,
+    /// Skip checking std if `rust.download-rustc` isn't available.
+    #[arg(global = true, long)]
+    pub skip_std_check_if_no_download_rustc: bool,
 }
 
 impl Flags {