requireFile: preferLocalBuild = true

There's no point trying to "distribute" showing the error message.

pkgs/build-support/trivial-builders.nix

···
       name = name_;
       outputHashAlgo = hashAlgo;
       outputHash = hash;
+      preferLocalBuild = true;
       builder = writeScript "restrict-message" ''
-source ${stdenv}/setup
-cat <<_EOF_
+        source ${stdenv}/setup
+        cat <<_EOF_
 
-***
-${msg}
-***
+        ***
+        ${msg}
+        ***
 
-_EOF_
+        _EOF_
       '';
     };