Fix CI on emscripten

Author: asomers

libc-test/build.rs

@@ -2895,6 +2895,9 @@ fn test_emscripten(target: &str) {
     });
 
     cfg.skip_struct(move |ty| {
+        if ty.starts_with("__c_anonymous_") {
+            return true;
+        }
         match ty {
             // This is actually a union, not a struct
             "sigval" => true,