Skip testing targets that don't ship libstd

tests/compiletest.rs

@@ -124,13 +124,27 @@ fn is_target_dir<P: Into<PathBuf>>(path: P) -> bool {
     path.metadata().map(|m| m.is_dir()).unwrap_or(false)
 }
 
+fn target_has_std<P: Into<PathBuf>>(path: P) -> bool {
+    let target_lib_dir = path.into().join("lib");
+    std::fs::read_dir(target_lib_dir)
+        .expect("invalid target")
+        .map(|entry| entry.unwrap())
+        .filter(|entry| entry.file_type().unwrap().is_file())
+        .filter_map(|entry| entry.file_name().into_string().ok())
+        .any(|file_name| file_name.starts_with("libstd") && file_name.ends_with(".rlib"))
+}
+
+
 fn for_all_targets<F: FnMut(String)>(sysroot: &Path, mut f: F) {
     let target_dir = sysroot.join("lib").join("rustlib");
     for entry in std::fs::read_dir(target_dir).expect("invalid sysroot") {
         let entry = entry.unwrap();
         if !is_target_dir(entry.path()) {
             continue;
         }
+        if !target_has_std(entry.path()) {
+            continue;
+        }
         let target = entry.file_name().into_string().unwrap();
         f(target);
     }