[tests] add test for generalized check

tests/spec/generalized_check.i

+/*@ check lemma tauto: \true ==> \true; */
+
+/*@ check requires \valid(x);
+    assigns *x;
+    check ensures *x == 0;
+*/
+void f(int* x) {
+  /*@ check \valid(x); */ // can't be proved by WP: we ignore the requires
+  *x = 0;
+}
+
+int main() {
+  int a = 4;
+  f(&a);
+  /*@ check a == 0; */ // can't be proved by WP: we ignore the ensures
+}

tests/spec/oracle/generalized_check.res.oracle

+[kernel] Parsing tests/spec/generalized_check.i (no preprocessing)
+/* Generated by Frama-C */
+/*@ check lemma tauto: \true;
+ */
+/*@ check requires \valid(x);
+    check ensures *\old(x) ≡ 0;
+    assigns *x; */
+void f(int *x)
+{
+  /*@ check \valid(x); */ ;
+  *x = 0;
+  return;
+}
+
+int main(void)
+{
+  int __retres;
+  int a = 4;
+  f(& a);
+  /*@ check a ≡ 0; */ ;
+  __retres = 0;
+  return __retres;
+}
+
+