ltlsynt: make sure the previous Xor optimization actually works

* spot/tl/simplify.hh, spot/tl/simplify.cc,
spot/twaalgos/translate.cc: Update the tl_simplification
options after all preferences have been given.
* bin/ltlsynt.cc: Display the size of the translation output.
* tests/core/ltlsynt.test: Add test case.

spot/tl/simplify.cc

@@ -4100,6 +4100,12 @@ namespace spot
     return simplify_recursively(f, cache_);
   }
 
+  tl_simplifier_options&
+  tl_simplifier::options()
+  {
+    return cache_->options;
+  }
+
   formula
   tl_simplifier::negative_normal_form(formula f, bool negated)
   {

spot/tl/simplify.hh

@@ -112,6 +112,14 @@ namespace spot
     /// constructor).
     formula simplify(formula f);
 
+#ifndef SWIG
+    /// The simplifier options.
+    ///
+    /// Those should can still be changed before the first formula is
+    /// simplified.
+    tl_simplifier_options& options();
+#endif
+
     /// Build the negative normal form of formula \a f.
     /// All negations of the formula are pushed in front of the
     /// atomic propositions.  Operators <=>, =>, xor are all removed