catdvi: fix generated code in configure script; fix darwin

add an int to generated main function to fix implicit int error

pkgs/tools/typesetting/tex/catdvi/default.nix

@@ -28,6 +28,11 @@ stdenv.mkDerivation (finalAttrs: {
     })
   ];
 
+  # fix implicit-int compile error in test code used in configure script
+  postPatch = ''
+    sed -i 's/^main()/int main()/' configure
+  '';
+
   hardeningDisable = [ "format" ];
 
   outputs = [ "out" ] ++ lib.optional (with stdenv; buildPlatform.canExecute hostPlatform) "dev";