[tests] checks that typing reject prog with two locals with same name and scope

even if one is ghost and the other non-ghost

tests/syntax/ghost_local_ill_formed.i

+void titi() {
+  int c = 0;
+    L0: ;
+    /* ill-formed: in ghost mode, we have two local c in the same scope. */
+    /*@ ghost int c = 1; */
+    L1: ;
+    c = 2;
+    /*@ assert c == 1; */
+    /*@ assert \at(c,L0) == 0; */
+    /*@ assert \at(c,L1) == 1; */
+  /*@ assert c == 2; */
+}

tests/syntax/oracle/ghost_local_ill_formed.res.oracle

+[kernel] Parsing tests/syntax/ghost_local_ill_formed.i (no preprocessing)
+[kernel] tests/syntax/ghost_local_ill_formed.i:5: User Error: 
+  redefinition of 'c' in the same scope.
+  Previous declaration was at tests/syntax/ghost_local_ill_formed.i:2
+[kernel] User Error: stopping on file "tests/syntax/ghost_local_ill_formed.i" that has errors.
+[kernel] Frama-C aborted: invalid user input.