Fix #3497: Add support for compiling in g++ 4.4 and 4.5

- Removed uses of lambda expressions

- Added custom defines for constexpr and nullptr

- Removed trailing comma of last value from generated enums

include/flatbuffers/idl.h

@@ -491,6 +491,10 @@ private:
   FLATBUFFERS_CHECKED_ERROR DoParse(const char *_source,
                                     const char **include_paths,
                                     const char *source_filename);
+  FLATBUFFERS_CHECKED_ERROR CheckClash(std::vector<FieldDef*> &fields,
+                                       StructDef *struct_def,
+                                       const char *suffix,
+                                       BaseType baseType);
 
  public:
   SymbolTable<StructDef> structs_;