cloog: enable parallel building, explicitly disable parallel testing

pkgs/development/libraries/cloog/default.nix

···
 
   configureFlags = [ "--with-isl=system" ];
 
-  # Breaks the test cases
-  #enableParallelBuilding = true;
+  enableParallelBuilding = true;
+  # Breaks the test cases as it reuses 'cloog_temp' file name for different tests.
+  enableParallelChecking = false;
 
   doCheck = true;