Include tags in type-to-identifier conversion

Within the same translation unit multiple incomplete structs/unions with
different names (tags) must be distinguished. Symbol numbering helps to keep
untagged types unique, but for tagged ones we need to take their names into
account.

Fixes: diffblue#4019

Author: tautschnig

regression/ansi-c/anonymous_union1/main.c

@@ -0,0 +1,20 @@
+int main()
+{
+  typedef struct onet
+  {
+    union {
+      struct onet *next;
+    } abc;
+  } onet;
+
+  typedef struct twot
+  {
+    union {
+      struct twot *next;
+    } xyz;
+  } twot;
+  twot two;
+
+  two.xyz.next->xyz.next = 0;
+  return 0;
+}

regression/ansi-c/anonymous_union1/test.desc

@@ -0,0 +1,8 @@
+CORE
+main.c
+
+^EXIT=0$
+^SIGNAL=0$
+--
+^warning: ignoring
+^CONVERSION ERROR$

src/ansi-c/type2name.cpp

@@ -44,40 +44,25 @@ static std::string type2name_tag(
      symbol->type.id()!=ID_union)
     return type2name(symbol->type, ns, symbol_number);
 
-  std::string result;
-
   // assign each symbol a number when seen for the first time
   std::pair<symbol_numbert::iterator, bool> entry=
     symbol_number.insert(std::make_pair(
         identifier,
         std::make_pair(symbol_number.size(), true)));
 
+  std::string result = "SYM" +
+                       id2string(to_struct_union_type(symbol->type).get_tag()) +
+                       '#' + std::to_string(entry.first->second.first);
+
   // new entry, add definition
   if(entry.second)
   {
-    result="SYM#"+std::to_string(entry.first->second.first);
     result+="={";
     result+=type2name(symbol->type, ns, symbol_number);
     result+='}';
 
     entry.first->second.second=false;
   }
-#if 0
-  // in recursion, print the shorthand only
-  else if(entry.first->second.second)
-    result="SYM#"+std::to_string(entry.first->second.first);
-  // entering recursion
-  else
-  {
-    entry.first->second.second=true;
-    result=type2name(symbol->type, ns, symbol_number);
-    entry.first->second.second=false;
-  }
-#else
-  // shorthand only as structs/unions are always symbols
-  else
-    result="SYM#"+std::to_string(entry.first->second.first);
-#endif
 
   return result;
 }