re2c: enable parallel building, enable tests

Parallel builds speed up building considerably.
Tests don't add much of an overhead.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

pkgs/development/tools/parsing/re2c/default.nix

@@ -13,6 +13,9 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [ autoreconfHook ];
 
+  doCheck = true;
+  enableParallelBuilding = true;
+
   preCheck = ''
     patchShebangs run_tests.sh
   '';