detect incompatible CI rustc options more precisely

src/bootstrap/src/core/download.rs

@@ -273,11 +273,12 @@ impl Config {
 
         let mut tar = tar::Archive::new(decompressor);
 
+        let is_ci_rustc = dst.ends_with("ci-rustc");
+
         // `compile::Sysroot` needs to know the contents of the `rustc-dev` tarball to avoid adding
         // it to the sysroot unless it was explicitly requested. But parsing the 100 MB tarball is slow.
         // Cache the entries when we extract it so we only have to read it once.
-        let mut recorded_entries =
-            if dst.ends_with("ci-rustc") { recorded_entries(dst, pattern) } else { None };
+        let mut recorded_entries = if is_ci_rustc { recorded_entries(dst, pattern) } else { None };
 
         for member in t!(tar.entries()) {
             let mut member = t!(member);
@@ -287,10 +288,12 @@ impl Config {
                 continue;
             }
             let mut short_path = t!(original_path.strip_prefix(directory_prefix));
-            if !short_path.starts_with(pattern) {
+            let is_builder_config = short_path.to_str() == Some("builder-config");
+
+            if !short_path.starts_with(pattern) && (is_ci_rustc && !is_builder_config) {
                 continue;
             }
-            short_path = t!(short_path.strip_prefix(pattern));
+            short_path = short_path.strip_prefix(pattern).unwrap_or(short_path);
             let dst_path = dst.join(short_path);
             self.verbose(|| {
                 println!("extracting {} to {}", original_path.display(), dst.display())