FIXME: Use a bigger hammer to try to see what CI is doing

Author: joshtriplett

libc-test/build.rs

@@ -2937,7 +2937,7 @@ fn test_freebsd(target: &str) {
 
             // __mcontext changed mc_spare and mc_tlsbase between OS releases, and `skip_field`
             // doesn't seem to work for them.
-            "__mcontext" => true,
+            t if t.contains("mcontext") => true,
 
             _ => false,
         }