Add names of the functions being wrapped to symbol table

At the very least this results in clear error messages when running SWIG if
the symbol is encountered twice instead of errors given only when compiling
the generated code later.

Source/Modules/c.cxx

@@ -1152,6 +1152,10 @@ ready:
    * ---------------------------------------------------------------------- */
    
   virtual int functionWrapper(Node *n) {
+    if (!Getattr(n, "sym:overloaded")) {
+      if (!addSymbol(Getattr(n, "sym:name"), n))
+	return SWIG_ERROR;
+    }
 
     if (CPlusPlus) {
          functionWrapperCPPSpecific(n);